¹ This organisation is also known as ‘the Islamic State of Iraq and the Levant’, ISIS (an acronym for ‘the Islamic State in Iraq and Greater Syria’), ISIL (an acronym for ‘the Islamic State in Iraq and the Levant’), Daesh (an abbreviation of the organisation's name in Arabic, al-dawlah al-islamiyah fil Iraq wa al-sham) or the Takfiri. For discussion see Raufer, Xavier, ‘The Islamic State, an Unidentified Terrorist Object’ (2016) 25 Polish Quarterly of International Affairs 45, 46Google Scholar; Cole Bunzel, ‘From Paper State to Caliphate: The Ideology of the Islamic State’, The Brookings Project on US Relations with the Islamic World, Analysis Paper No 19, 3 March 2015, https://www.brookings.edu/wp-content/uploads/2016/06/The-ideology-of-the-Islamic-State-1.pdf.

² For discussion see Raufer (n 1) 46; Kadercan, Burak, ‘What the ISIS Crisis Means for the Future of the Middle East’ (2016) 18 Insight Turkey 63, 64–67.Google Scholar

³ McCants, William, The ISIS Apocalypse: The History, Strategy, and Doomsday Vision of the Islamic State (St Martin's Press 2015) 121Google Scholar; Coco, Antonio and Maillart, Jean-Baptiste, ‘The Conflict with Islamic State: A Critical Review of International Legal Issues’ in Bellal, Annyssa (ed), The War Report: Armed Conflict in 2014 (Oxford University Press 2015) 388, 389Google Scholar; Kajtar, Gabor, ‘The Use of Force against ISIL in Iraq and Syria: A Legal Battlefield’ (2017) 34 Wisconsin International Law Journal 535, 543Google Scholar.

⁴ UNSC Res 2170 (15 August 2014), UN Doc S/RES/2170; UNSC Res 2249 (20 November 2015), UN Doc S/RES/2249.

⁵ Waltman, Gerald III, ‘Prosecuting ISIS’ (2016) 85 Mississippi Law Journal 817, 826–27Google Scholar; Hassan Hassan, ‘The Sectarianism of the Islamic State: Ideological Roots and Political Context’, Carnegie Middle East Center, 13 June 2016, http://carnegie-mec.org/2016/06/13/sectarianism-of-islamic-state-ideological-roots-and-political-context/j1sf; Haroon Siddique, ‘20,000 Iraqis Besieged by Isis Escape from Mountain after US Air Strikes’, The Guardian, 10 August 2014, http://www.theguardian.com/world/2014/aug/10/iraq-yazidi-isis-jihadists-islamic-state-kurds.

⁶ Jackson, Aaron L, ‘Hunting Down Terrorists “Wherever They Exist”: ISIL in Syria and the Legal Argument for United States Military Operations Within the Territory of a Non-Consenting Nation-State’ (2015) 74 Air Force Law Review 133, 134Google Scholar; Ali, Al-Ghafli, ‘The Islamic Military Alliance to Fight Terrorism: Structure, Mission, and Politics’ (2017) 12 Journal of Regional Security 157Google Scholar.

⁷ While significant support was expressed for these coalitions, some states did not support them. In particular, Russia was not willing to support any operations without authorisation, and additional criticism was raised by Ecuador, Iran and Argentina. For discussion see Starski, Paulina, ‘Right to Self-Defense, Attribution and the Non-State Actor: Birth of the “Unable or Unwilling” Standard?’ (2015) 75 ZaöRV 455, 488Google Scholar.

⁸ Seth G Jones and others, Rolling Back the Islamic State (RAND Corporation 2017) 13–39, https://www.rand.org/content/dam/rand/pubs/research_reports/RR1900/RR1912/RAND_RR1912.pdf.

⁹ Margaret Coker, Eric Schmitt and Rukmini Callimachi, ‘With Loss of Its Caliphate, ISIS May Return to Guerrilla Roots’, New York Times, 18 October 2017, https://www.nytimes.com/2017/10/18/world/middleeast/islamic-state-territory-attacks.html?rref=collection%2Ftimestopic%2FIslamic%20State%20in%20Iraq%20and%20Syria%20(ISIS)&_r=0.

¹⁰ Jin Wu, Derek Watkins and Rukmini Callimachi, ‘ISIS Lost Its Last Territory in Syria. But the Attacks Continue’, New York Times, 23 March 2019, https://www.nytimes.com/interactive/2019/03/23/world/middleeast/isis-syria-defeated.html?rref=collection%2Ftimestopic%2FIslamic%20State%20in%20Iraq%20and%20Syria%20(ISIS).

¹¹ UNSC, Letter dated 23 September 2014 from the Permanent Representative of the United States of America to the United Nations addressed to the Secretary-General (23 September 2014), UN Doc S/2014/695.

¹² James A Green, ‘Initial Thoughts on the UK Attorney General's Self-Defence Speech’, EJIL: Talk!, 13 January 2017, https://www.ejiltalk.org/initial-thoughts-on-the-uk-attorney-generals-self-defence-speech.

¹³ UNSC, Letter dated 9 September 2015 from the Permanent Representative of Australia to the United Nations addressed to the President of the Security Council (9 September 2015), UN Doc S/2015/693.

¹⁴ UNSC, Letter dated 31 March 2015 from the Chargé d'Affaires a.i. of the Permanent Mission of Canada to the United Nations addressed to the President of the Security Council (31 March 2015), UN Doc S/2015/221.

¹⁵ UNSC, Letter dated 24 July 2015 from the Chargé d'Affaires a.i. of the Permanent Mission of Turkey to the United Nations addressed to the President of the Security Council (24 July 2015), UN Doc S/2015/563.

¹⁶ The concept of sovereignty was first introduced in 1576 by Bodin, and later affirmed in the Treaties of Westphalia of 1648, which recognised the right of (Western) states to establish a domestic governmental system without outside interference from other states. The strength of sovereignty grew alongside the modern nation-state system, and today sovereignty is a foundational principle in the international system in which states were, and still are, the predominant actors: see Island of Palmas Case (Netherlands v US) 2 RIAA 829–71 (1928); Spruyt, Hendrik, The Sovereign State and its Competitors: An Analysis of Systems Change (Princeton University Press 1994)Google Scholar; Koskenniemi, Martti, The Gentle Civilizer of Nations: The Rise and Fall of International Law 1870–1960 (Cambridge University Press 2001) 11CrossRefGoogle Scholar; Mégret, Frédéric, ‘International Law as Law’ in Crawford, James and Koskenniemi, Martti (eds), The Cambridge Companion to International Law (Cambridge University Press 2012) 64, 66Google Scholar; French, Duncan, ‘Introduction’ in French, Duncan (ed), Statehood and Self-Determination: Reconciling Tradition and Modernity in International Law (Cambridge University Press 2013) 1–21CrossRefGoogle Scholar; Yaël Ronen, ‘Entities that Can Be States but Do Not Claim To Be’ in French, ibid 23.

¹⁷ Legal Consequences of the Construction of a Wall in the Occupied Palestinian Territory, Advisory Opinion [2004] ICJ Rep 136, separate opinion of Judge Elaraby [74]; Gray, Christine, ‘The Use of Force and the International Legal Order’ in Evans, Malcolm D (ed), International Law (Oxford University Press 2010) 617Google Scholar.

¹⁸ Charter of the United Nations (entered into force 24 October 1945) 1 UNTS XVI (UN Charter).

¹⁹ eg, Simma, Bruno, ‘NATO, the UN and the Use of Force’ (1999) 10 European Journal of International Law 1CrossRefGoogle Scholar.

²⁰ For discussion see Kajtar (n 3) 573; Stahn, Carsten, ‘Terrorist Acts as “Armed Attack”: The Right to Self-Defense, Article 51(1/2) of the UN Charter and International Terrorism’ (2003) 27 Fletcher Forum of World Affairs 35, 36Google Scholar; Franck, Thomas M, ‘Terrorism and the Right of Self-Defense’ (2001) 95 American Journal of International Law 839, 840CrossRefGoogle Scholar; Katja Samuel, ‘Can Religious Norms Influence Self-Determination Struggles, and with What Implications for International Law?’ in French (n 16) 306; Gray, Christine, International Law and the Use of Force (3rd edn, Oxford University Press 2008) 130, 135–38Google Scholar; UNGA Res 42/159 (7 December 1987), UN Doc A/RES/42/159, para 14; UNGA Res 1514 (XV), Declaration on the Granting of Independence to Colonial Countries and Peoples (14 December 1960), UN Doc A/RES/1514(XV), paras 1–2, 4.

²¹ UN Charter (n 18) 2 para 7; Military and Paramilitary Activities in and against Nicaragua (Nicaragua v US), Merits, [1986] ICJ Rep 14, [202]; Kelly, Lyndsey, ‘The Downfall of the Responsibility to Protect: How the Libyan and Syrian Crises Secured the Fate of the Once-Emerging Norm’ (2016) 43 Syracuse Journal of International Law and Commerce 381, 392Google Scholar. See Island of Palmas Case (n 16); SS ‘Lotus’ (France v Turkey) (1927) PCIJ (Ser A No 3); Brand, Ronald A, ‘The Role of International Law in the Twenty-First Century: External Sovereignty and International Law’ (1995) 18 Fordham International Law Journal 1685, 1686Google Scholar; Mégret (n 16); Cohan, John Alan, ‘Sovereignty in a Postsovereign World’ (2006) 18 Florida Journal of International Law 907.Google Scholar

²² Grim, Ditter, ‘The State Monopoly on the Use of Force’ in Heitmeyer, Wilhelm and Hagan, John (eds), International Handbook of Violence Research (Springer 2005) 1043Google Scholar; Nicholas Tsagourias, ‘Non-State Actors in International Peace and Security: Non-State Actors and the Use of Force’ in Jean d'Aspremont, Michael William Reisman and Math Noortmann (eds), Participants in the International Legal System: Multiple Perspectives on Non-State Actors in International Law (2011) 326. Historically, Hobbes believed that the only way for people to live in civil peace and social unity is under a social contract allowing the rule of an absolute sovereign, which is able to monopolise the use of force: Hobbes, Thomas, Leviathan xxxix (Michael Oakeshott ed, 1950)Google Scholar. In pursuance, it was stated by Weber that a state is a human community that successfully claims the monopoly of the legitimate use of physical force within a given territory: Weber, Max, From Max Weber: Essays in Sociology (Routledge 1946) 77Google Scholar.

²³ Eyal Benvenisti and Doreen Lustig, ‘Taming Democracy: Codifying the Laws of War to Restore the European Order, 1856–1874’ (2017) University of Cambridge Faculty of Law Research Paper No. 28/2017, https://ssrn.com/abstract=2985781. Another example is the 1856 Declaration of Paris, which took back authorisation on the use of force given to privateers, by banning it and, in a way, reversing the privatisation of the colonial enterprise.

²⁴ Fisheries Jurisdiction (Spain v Canada) [1998] ICJ Rep 432, 466.

²⁵ In the view of Jackson (n 6) 161, receiving consent will be the optimal approach.

²⁶ Cheng, Bin, General Principles of Law as Applied by International Courts and Tribunals (Stevens for the London Institute of World Affairs 1953) 88–96Google Scholar.

²⁷ See, eg, Simma (n 19).

²⁸ Brownlie, Ian, International Law and the Use of Force by States (Oxford University Press 1963) 364CrossRefGoogle Scholar. For a modern view of this prohibition see Roscini, Marco, ‘Threats of Armed Force and Contemporary International Law’ (2007) 54 Netherlands International Law Review 229, 234–35CrossRefGoogle Scholar.

²⁹ Armed Activities on the Territory of the Congo (Democratic Republic of the Congo v Uganda) [2005] ICJ Rep 168; Roscini (n 28). For discussion relating to collective self-defence see Schachter, Oscar, International Law in Theory and Practice (Martinus Nijhoff 1997) 155Google Scholar; Gray (n 17) 632.

³⁰ This customary right was recognised, inter alia, in the Nicaragua case: Nicaragua v US (n 21) [190].

³¹ There are several alleged customary exceptions, such as humanitarian intervention. Another exception is the protection of nationals whose lives are at risk abroad. The most controversial exception is probably the claim that states can assist people fighting for their right to self-determination. For discussion see Brownlie (n 28); Gray (n 17) 615; Gray (n 20); Cooper, Matthew C, ‘A Note to States Defending Humanitarian Intervention: Examining Viable Arguments before the International Court of Justice’ (2012) 40 Denver Journal of International Law and Policy 167Google Scholar.

³² Scharf, Michael P, ‘How the War Against ISIS Changed International Law’ (2016) 48 Case Western Reserve Journal of International Law 1, 22Google Scholar; Anne Peters, ‘The Turkish Operation in Afrin (Syria) and the Silence of the Lambs’, EJIL: Talk!, 30 January 2018, https://www.ejiltalk.org/the-turkish-operation-in-afrin-syria-and-the-silence-of-the-lambs. The scale and effects criteria is not necessarily connected with numbers; rather it is a legal assessment depending on the facts and circumstances at hand: see Lokman B Çetinkaya, ‘Turkey's Military Operations in Syria’, EJIL: Talk!, 20 February 2018, https://www.ejiltalk.org/turkeys-military-operations-in-syria.

³³ The scope, duration and intensity would be of importance in assessing proportionality. As for necessity, the main element in this regard is the imminence of the need to respond and the evaluation of other alternatives. For elaboration see Lubell, Noam, ‘The Problem of Imminence in an Uncertain World’ in Weller, Marc (ed), The Oxford Handbook of the Use of Force in International Law (Oxford University Press 2015) 697Google Scholar; Çetinkaya (n 32).

³⁴ Nicaragua v US (n 21) [191]; Michael N Schmitt and Andru E Wall, ‘The International Law of Unconventional Statecraft’ (2014) 5 Harvard National Security Journal 349, 359.

³⁵ For elaboration see Zweifach, Benjamin, ‘Plugging the Gap: A Reconsideration of the U.N. Charter's Approach to Low-Gravity Warfare’ (2013) 8 Intercultural Human Rights Law Review 379Google Scholar. See also Jackson (n 6) 167; Lekas, Annalise, ‘ISIS: The Largest Threat to World Peace Trending Now’ (2015) 30 Emory International Law Review 313, 332–35Google Scholar.

³⁶ Peters (n 32).

³⁷ Nicaragua v US (n 21) [249].

³⁸ Oil Platforms (Iran v US) [2003] ICJ Rep 161, separate opinion of Judge Simma, [12] (‘I would suggest a distinction between (full-scale) self-defence within the meaning of Article 51 against an “armed attack” within the meaning of the same Charter provision on the one hand and, on the other, the case of hostile action, for instance against individual ships, below the level of Article 51, justifying proportionate defensive measures on the part of the victim, equally short of the quality and quantity of action in self-defence expressly reserved in the United Nations Charter. Here I see a certain analogy with the Nicaragua case, where the Court denied that the hostile activities undertaken by Nicaragua against El Salvador amounted to an “armed attack” within the meaning of Article 51, that would have given the United States a right to engage in collective self-defence, and instead qualified these activities as illegal military intervention. What the Court did consider permissible against such unlawful acts were “proportionate counter-measures”, but only those resorted to by the immediate victim’).

³⁹ Oil Platforms (Iran v US), ibid, separate opinion of Judge Higgins, [43] (‘Whether the Court envisaged only non-forceful countermeasures is, for the moment, a matter of conjecture. That, too, is not addressed in the present judgment. The Court simply moves on from the Court's 1986 statement that a necessary measure to protect essential security interests could be action taken in self-defence’).

⁴⁰ ILC, Articles on Responsibility of States for Internationally Wrongful Acts, with Commentaries (2001) UN Doc A/56/10 (2001) (ARSIWA) art 22.

⁴¹ For discussion see Proukaki, Elena Katselli, The Problem of Enforcement in International Law (Routledge 2010) 221Google Scholar; Corn Products International Inc v Mexico, ICSID Case No ARB(AF)/04/01, para 145 (2008); Gabčíkovo-Nagymaros Project, Advisory Opinion [1997] ICJ Rep 7, dissenting opinion of Judge Vereshchetin, [83]; Responsibility of Germany for Damage Caused in the Portuguese Colonies in the South of Africa (Naulilaa Incident) (Portugal v Germany) II RIAA 1011, 1028 (1928).

⁴² ARSIWA (n 40) art 50(1)(a). See Bederman, David J, ‘Counterintuiting Countermeasures’ (2002) 96 American Journal of International Law 817CrossRefGoogle Scholar; Cannizzaro, Enzo, ‘The Role of Countermeasures in the Law of International Countermeasures’ (2001) 12 European Journal of International Law 889CrossRefGoogle Scholar. For further discussion see Starski (n 7) 467.

⁴³ ARSIWA (n 40) art 25.

⁴⁴ Gabčíkovo-Nagymaros Project (n 41) [51]–[52].

⁴⁵ Enron v Argentina (2007) ICSID Case No ARB/01/3, para 308.

⁴⁶ UNSC Res 2268 (26 February 2016), UN Doc S/RES/2268, para 2; UNSC Res 2254 (18 December 2015), UN Doc S/RES/2254, para 2.

⁴⁷ Liz Fields, ‘UNICEF Wants State Officials to Negotiate with Islamic State to Help Aid Delivery’, Vice News, 13 March 2015, https://news.vice.com/article/unicef-wants-state-officials-to-negotiate-with-islamic-state-to-help-aid-delivery.

⁴⁸ ARSIWA (n 40) commentary to art 25, para 19.

⁴⁹ UN Charter (n 18) art 2(7); Schmitt and Wall (n 34) 354.

⁵⁰ Schachter, Oscar, ‘International Law in Theory and Practice’ (1982) 178 Recueil des Cours 160Google Scholar. For more discussion in the same vein see Schachter (n 29) 158.

⁵¹ Schmitt and Wall (n 34) 355.

⁵² Nicaragua v US (n 21) [205].

⁵³ Other terms parallel with ‘coercive’ are ‘forcible’ or ‘dictatorial’: see Jennings, Robert and Watts, Arthur (eds), Oppenheim's International Law (9th edn, Oxford University Press 1992) 43Google Scholar.

⁵⁴ Philip Kunig, ‘Intervention, Prohibition of’, The Max Planck Encyclopedia of Public International Law 1, para 4, https://opil.ouplaw.com/view/10.1093/law:epil/9780199231690/law-9780199231690-e1434?prd=EPIL; Lieblich, Eliav, ‘Intervention and Consent: Consensual Forcible Interventions in Internal Armed Conflicts as International Agreements’ (2011) 29 Boston University International Law Journal 337Google Scholar.

⁵⁵ Nicaragua v US (n 21) [205], [242]; Democratic Republic of the Congo v Uganda (n 29) [165]; Declaration on Principles of International Law Concerning Friendly Relations and Co-operation among States in Accordance with the Charter of the United Nations, UNGA Res 2625 (XXV) (24 October 1970), UN Doc A/RES/2625. For more discussion relating to intervention in civil wars see Gray (n 17) 623.

⁵⁶ Nicaragua v US (n 21) [243]; Schmitt and Wall (n 34) 361.

⁵⁷ Nicaragua v US (n 21) [243]; For further discussion see Lieblich (n 54).

⁵⁸ For discussion see Schmitt, Michael N, The Tallinn Manual on the International Law Applicable to Cyber Warfare (Cambridge University Press 2013) 47CrossRefGoogle Scholar; Gill, Terry, ‘Non-Intervention in the Cyber Context’ in Ziolkowski, Katharina (ed), Peacetime Regime for State Activities in Cyberspace (NATO CCD COE Publication 2013) 234Google Scholar.

⁵⁹ Longo, Christine, ‘R2P: An Efficient Means for Intervention in Humanitarian Crises: A Case Study of ISIL in Iraq and Syria’ (2016) 48 The George Washington International Law Review 893, 896Google Scholar.

⁶⁰ Henkin, Louis, ‘That “S” Word: Sovereignty, and Globalization, and Human Rights, Et Cetera’ (1999) 68(1) Fordham Law Review 1, 10Google Scholar.

⁶¹ Accordance with International Law of the Unilateral Declaration of Independence in respect of Kosovo, Advisory Opinion [2010] ICJ Rep 403, [80].

⁶² For discussion see Finucane, Brian, ‘Fictitious States, Effective Control, and the Use of Force Against Non-State Actors’ (2012) 30 Berkeley Journal of International Law 35Google Scholar; Printer, Norman G, ‘The Use of Force Against Non-State Actors under International Law: An Analysis of the U.S. Predator Strike in Yemen’ (2013) 8 UCLA Journal of International Law and Foreign Affairs 331Google Scholar.

⁶³ UNSC Res 1368 (12 September 2001), UN Doc S/RES/1368; UNSC Res 1373 (28 September 2001), UN Doc S/RES/1373; UNSC Res 1438 (14 October 2002), UN Doc S/RES/1438; UNSC Res 1530 (11 March 2004), UN Doc S/RES/1530.

⁶⁴ Legal Consequences of the Construction of a Wall (n 17) [139] (‘Article 51 of the Charter thus recognizes the existence of an inherent right of self-defence in the case of armed attack by one State against another State. However, Israel does not claim that the attacks against it are imputable to a foreign State’). A different view was presented by three judges on the panel, according to which there is nothing in the text of Article 51 that stipulates that self-defence is available only when an armed attack is made by a state, or that excludes the application of this article against attacks by an NSA. See ibid para 33 of the separate opinion of Judge Higgins, para 35 of the separate opinion of Judge Kooijmans, and para 6 of the declaration of Judge Buergenthal. A similar view to that of the majority was evidenced in Armed Activities on the Territory of the Congo (n 29) [146]–[147]. In this instance, Judge Simma noted (para 11 of his separate opinion) the practice of the Security Council which allowed for the use of force against an NSA.

⁶⁵ Kajtar (n 3) 573; see also Gray (n 20) 135–38.

⁶⁶ See, eg, Murphy, Sean D, ‘Terrorism and the Concept of “Armed Attack” in Article 51 of the U.N. Charter’ (2002) 43 Harvard International Law Journal 41, 47–51Google Scholar; Stahn (n 20) 36; Franck (n 20) 840; Zemanek, Karl, ‘Response to a Terrorist Attack: A Clarification of Issues’ (2013) 15 Austrian Review of International and European Law 199, 209Google Scholar. For elaboration about the suggestion in the German parliament that customary international law evolved in a way that allows the attacking of an NSA, see Anne Peters, ‘German Parliament Decides to Send Troops to Combat ISIS − Based on Collective Self-Defence “in Conjunction with” SC Res. 2249’, EJIL: Talk!, 8 December 2015, https://www.ejiltalk.org/german-parlament-decides-to-send-troops-to-combat-isis-%E2%88%92-based-on-collective-self-defense-in-conjunction-with-sc-res-2249.

⁶⁷ Jackson (n 6) 161; Cheng (n 26).

⁶⁸ Schachter (n 29) 119.

⁶⁹ Tsagourias (n 22) 327.

⁷⁰ Corten, Olivier, The Law Against War: The Prohibition on the Use of Force in Contemporary International Law (Hart 2010) 311–401Google Scholar.

⁷¹ Draft Proposal Submitted by Australia, Canada, Italy, Japan, the United Kingdom of Great Britain and Northern Ireland and the United States of America (25 March 1969), UN Doc A/AC/.134/L.17.

⁷² UNGA Res 3314 (XXIX) (14 December 1974), UN Doc A/RES/3314(XXIX).

⁷³ Rome Statute of the International Criminal Court (entered into force 1 July 2002) 2187 UNTS 90, art 8 bis.

⁷⁴ Tams, Christian J, ‘Self-Defence against Non-State Actors: Making Sense of the “Armed Attack” Requirement’ in O'Connell, Mary Ellen, Tams, Christian J and Tladi, Dire, Self-Defence against Non-State Actors (Cambridge University Press 2019) 132Google Scholar.

⁷⁵ UNGA Res 3314 (n 72).

⁷⁶ ibid, art 7.

⁷⁷ Samuel (n 20).

⁷⁸ Wolfrum, Rüdiger and Philipp, Christiane E, The Status of the Taliban: Their Obligations and Rights under International Law (Kluwer Law International 2002) 585Google Scholar.

⁷⁹ UNGA Res 1514 (n 20) paras 1–2, 4.

⁸⁰ UNGA Res 2105 (XX) (20 December 1965), UN Doc A/RES/2105(XX); UNGA Res 2625 (XXV) (n 55).

⁸¹ UNGA Res 2787 (XXVI) ( 6 December 1971), UN Doc A/RES/2787, para 4.

⁸² UNGA Res 42/159 (n 20) para 14.

⁸³ Tsagourias (n 22) 327.

⁸⁴ Legal Consequences of the Construction of a Wall (n 17) separate opinion of Judge Elaraby, [3.1]; Nicaragua v US (n 21); Gray (n 17) 617.

⁸⁵ Reparation for Injuries Suffered in the Service of the United Nations, Advisory Opinion [1949] ICJ Rep 174, 178.

⁸⁶ Jackson (n 6) 142; Raufer (n 1) 46; Waltman (n 5). The organisation was originally created by Abu Musab Al-Zarqawi, under the name of Jama'at al-Tawhid w'al-Jihad in 2003, and it was later commissioned by Osama bin Laden as Al-Qaeda in Iraq. After the death of Al-Zarqawi in 2006, it renamed itself as the Islamic State in Iraq (ISI). For discussion see Kadercan (n 2) 64–67. For an elaborated account of the caliphate project see McCants (n 3); Warrick, Joby, Black Flags: The Rise of ISIS (Doubleday 2016)Google Scholar.

⁸⁷ Michael Weiss and Hassan, ISIS: Inside the Army of Terror (Regan Arts 2016) 169.

⁸⁸ UN Security Council, Report of the Secretary-General on the Threat posed by ISIL (Da'esh) to International Peace and Security and the Range of United Nations Efforts in Support of Member States in Countering the Threat (29 January 2016), UN Doc S/2016/92, 2.

⁸⁹ UN Human Rights Council, Report of the Independent International Commission of Inquiry on the Syrian Arab Republic (5 February 2015), UN Doc A/HRC/28/69, [36]. The Islamic State's vision of statehood has drawn inspiration from Wahhabism, a doctrine that promotes political organisation as a religious monotheistic state and was wedded into Saudi Arabia's political establishment: see McCants (n 3) 121; Delahunty, Robert J, ‘An Epitaph for ISIS: The Idea of a Caliphate and the Westphalian Order’ (2018) 35 Arizona Journal of International and Comparative Law 1, 36Google Scholar.

⁹⁰ Helen Lock, ‘How Isis Became the Wealthiest Terror Group in History’, Independent, 15 September 2014, http://www.independent.co.uk/news/world/middle-east/how-isis-became-the-wealthiest-terror-group-in-history-9732750.html; Nadan Feldman, ‘How ISIS Became the World's Richest Terror Group’, Ha'aretz, 10 November 2015, http://www.haaretz.com/middle-east-news/isis/1.686287. The organisation was also very well equipped militarily: for example, it had more tanks than the French army: see Raufer (n 1) 46. For an elaboration of the economic capabilities of the Islamic State from a historical perspective, see Patrick B Johnston and others, Foundations of the Islamic State: Management, Money, and Terror in Iraq, 2005–2010 (RAND 2016). See also Ben Smith, ‘ISIS and the Sectarian Conflict in the Middle East’, HC Library Research Paper No 15/16, 2015, http://researchbriefings.files.parliament.uk/documents/RP15-16/RP15-16.pdf.

⁹¹ At the time of the declaration relating to the establishment of the Caliphate, the Islamic State controlled territory stretching from Mosul to the outskirts of Aleppo in Syria, which is more or less the distance between Washington DC and Cleveland, Ohio: see McCants (n 3) 121.

⁹² See Lekas (n 35) 321; Jackson (n 6) 145. For discussion on the spreading of ISIS into other states, see Smith (n 90). For a look at the economic capabilities of the Islamic State, from a historical perspective, see Johnston and others (n 90). For data on the number of foreign fighters in the Islamic State, see ‘Foreign Fighters: An Updated Assessment of the Flow of Foreign Fighters into Syria and Iraq’, The Soufan Group, 2 December 2015, https://wb-iisg.com/wp-content/uploads/bp-attachments/4826/TSG_ForeignFightersUpflow.pdf.

⁹³ Wahhabism is the intellectual legacy of the thirteenth century Islamic scholar Taqi al-Din Ibn Taymiyyah, as interpreted and enforced by Ibn Abd al-Wahhab and his successors. For discussion see Hassan (n 5); Fouad al-Ibrahim, ‘Why ISIS Is a Threat to Saudi Arabia: Wahhabism's Deferred Promise, Alakhbar English, 22 August 2014, http://serpent-libertaire.over-blog.com/2014/08/why-isis-is-a-threat-to-saudi-arabia-wahhabism-s-deferred-promise.html.

⁹⁴ Kajtar (n 3) 548; Stern, Jessica, ‘Radicalization to Extremism and Mobilization to Violence: What Have We Learned and What Can We Do about It?’ (2016) 668 Annals 102, 106Google Scholar.

⁹⁵ For discussion of the secular basis of the current international order see Lilla, Mark, The Stillborn God: Religion, Politics, and the Modern West (Penguin Random House 2008) 7Google Scholar. The goal of the Islamic State is to monopolise Sunni political representation and disseminate monotheism. This wish is based on the concept of bidah, an Islamic term which forbids the inventing of religious practices unsanctioned by the religion, which is used to label practices, largely Sufi and Shia, as polytheistic: see Hassan (n 5); see also Bellew, Chelsea Elizabeth, ‘Secession in International Law: Could ISIS Become a Legally Recognized State?’ (2015) 42 Ohio Northern University Law Review 239, 259Google Scholar; Stern (n 94) 107.

⁹⁶ Waltman (n 5) 826–27; Hassan (n 5); Siddique (n 5).

⁹⁷ Jackson (n 6) 134.

⁹⁸ US Department of Defense, Press Release, ‘Statement by Pentagon Press Secretary Rear Admiral John Kirby on Airstrikes in Iraq’, 10 August 2014, http://www.defense.gov/Releases/Release.aspx?ReleaseID=16878.

⁹⁹ Air strikes in Syria focused on significant strongholds as well as strategic targets, such as oil fields: see Jackson (n 6) 134; Claudette Roulo, ‘U.S. Begins Airstrikes Against ISIL in Syria’, US Department of Defense, 22 September 2014, http://www.defense.gov/news/newsArticle.aspx?id=123233.

¹⁰⁰ Jackson, ibid.

¹⁰¹ Kadercan (n 2) 78–80.

¹⁰² UNSC Press Release, ‘Security Council Al-Qaida Sanctions Committee Amends Three Entries on Its Sanctions List’ (2 June 2014), SC/11424.

¹⁰³ Kajtar (n 3) 556. Pursuant to this request, Russia began missile strikes in Syria on 30 September 2015 and continues to support the Syrian government until now: see, eg, UN Security Council, Letter dated 15 October 2015 from the Permanent Representative of the Russian Federation to the United Nations addressed to the President of the Security Council (15 October 2015), UN Doc S/2015/792.

¹⁰⁴ There have been numerous NSAs involved in the Syrian civil war, including, but not only the following: The Free Syrian Army; Ahrar Al-Sham Coalition; Jaish Al-Islam; Katazb Thuwar Al Sham; Jaish Al-Islam; Shamia Front; Mujahidi Ibn Taimia; Liwa Miqdad Bin Amro; Jaish Al-Mujahidin; Tajamu Fastaqim Kama Umirt; Sukour Al-Sham; Jabhat al-Nusra (The Nusra Front); Kurdish Democratic Unity Party; Popular Protection Units; National Coalition of Revolutionary and Opposition Forces.

¹⁰⁵ For discussion see Kajtar (n 3) 540.

¹⁰⁶ UN Security Council, Letter dated 25 June 2014 from the Permanent Representative of Iraq to the United Nations addressed to the Secretary General (25 June 2014), UN Doc S/2014/440 (‘We therefore request urgent assistance from the international community’); UN Security Council, Letter dated 20 September 2014 from the Permanent Representative of Iraq to the United Nations addressed to the President of Security Council (20 September 2014), UN Doc S/2014/691 (‘It is for these reasons that we, in accordance with international law and the relevant bilateral and multilateral agreements, and with due regard for complete national sovereignty and the Constitution, have requested the United States of America to lead international efforts to strike ISIL sites and military strongholds, with our express consent … We are grateful for the international community's support and believe that the provision of additional assistance for the specific purpose of targeting ISIL will further help the Iraqi people and the security forces to turn the tide in the struggle against the terrorists, and thereby restore security and stability in our territory’).

¹⁰⁷ Schachter (n 29) 114; ARSIWA (n 40) art 20(1). For further discussion see Crawford, James, The International Law Commission's Articles on State Responsibility: Introduction, Text and Commentaries (Cambridge University Press 2002)Google Scholar ARSIWA, ibid, commentary to art 20(1), 72–74.

¹⁰⁸ UN Security Council, Identical Letters dated 17 September 2015 from the Permanent Representative of the Syrian Arab Republic to the United Nations addressed to the Secretary-General and the President of the Security Council (21 September 2015), UN Doc S/2015/719; UN Security Council, Identical Letters dated 18 September 2015 from the Permanent Representative of the Syrian Arab Republic to the United Nations addressed to the Secretary-General and the President of the Security Council (22 September 2015), UN Doc S/2015/727; Ryan Goodman, ‘Taking the Weight off of International Law: Has Syria Consented to US Airstrikes’, Just Security, 23 December 2014, http://justsecurity.org/18665/weightinternational-law-syria-consented-airstrikes/.

¹⁰⁹ UNSC, Letter dated 15 October 2015 (n 103). For elaboration see Kajtar (n 3) 556.

¹¹⁰ The attacks took place, inter alia, in the vicinity of the Stade de France (football stadium) while it hosted a national team game with many spectators, including the French President François Hollande, as well as on the streets of Paris and Le Petit Cambodge and Le Carillon restaurants. The deadliest part of the attack took place at a rock performance at the Bataclan Theatre. The Islamic State justified the attack as a response to French participation in the coalition operating against the group: for discussion see Marko Milanovic, ‘France Derogates from ECHR in the Wake of the Paris Attacks’, EJIL: Talk!, 13 December 2015, http://www.ejiltalk.org/france-derogates-from-echr-in-the-wake-of-the-paris-attacks; Marc Weller, ‘Permanent Imminence of Armed Attacks: Resolution 2249 (2015) and the Right to Self Defence Against Designated Terrorist Groups’, EJIL: Talk!, 25 November 2015, http://www.ejiltalk.org/permanent-imminence-of-armed-attacks-resolution-2249-2015-and-the-right-to-self-defence-against-designated-terrorist-groups.

¹¹¹ For elaboration see Karen Yourish and others, ‘How Many People Have Been Killed in ISIS Attacks Around the World’, New York Times, 16 July 2016, https://www.nytimes.com/interactive/2016/03/25/world/map-isis-attacks-around-the-world-DE.html; Kadercan (n 2) 64; Tim Lister and others, ‘ISIS Goes Global: 143 Attacks in 29 Countries Have Killed 2,043’, CNN, 12 February 2018, https://edition.cnn.com/2015/12/17/world/mapping-isis-attacks-around-the-world/index.html.

¹¹² US Department of Defense (n 98); Dapo Akande and Zachary Vermeer, ‘The Airstrikes against Islamic State in Iraq and the Alleged Prohibition on Military Assistance to Governments in Civil Wars’, EJIL: Talk!, 2 February 2015, http://www.ejiltalk.org/theairstrikes-against-islamic-state-in-iraq-and-the-alleged-prohibition-on-military-assistance-to-governments-in-civilwars; Raphael Van Steenberghe, ‘The Alleged Prohibition on Intervening in Civil Wars Is Still Alive after the Airstrikes against Islamic State in Iraq: A Response to Dapo Akande and Zachary Vermeer’, EJIL: Talk!, 12 February 2015, http://www.ejiltalk.org/the-alleged-prohibition-on-intervening-in-civil-wars-is-still-alive-after-theairstrikes-against-islamic-state-in-iraq-a-response-to-dapo-akande-and-zachary-vermeer.

¹¹³ From August 2014 to March 2015 the coalition conducted 1,700 air strikes in Iraq, and the US conducted 946 air strikes in Syria: Lekas (n 35) 324; Laura Visser, ‘Russia's Intervention in Syria’, EJIL: Talk!, 25 November 2015, http://www.ejiltalk.org/russias-intervention-in-syria; Dapo Akande, ‘Embedded Troops and the Use of Force in Syria: International and Domestic Law Questions’, EJIL: Talk!, 11 September 2015, http://www.ejiltalk.org/embedded-troops-and-the-use-of-force-in-syria-international-and-domestic-law-questions.

¹¹⁴ Jake Rylatt, ‘The Use of Force against ISIL in Libya and the Sounds of Silence’, EJIL: Talk!, 6 January 2016, http://www.ejiltalk.org/the-use-of-force-against-isil-in-libya-and-the-sounds-of-silence.

¹¹⁵ Jackson (n 6) 156; Roulo (n 99).

¹¹⁶ Participating aircraft included F-15, F-16, F/A-18, F-22 fighter aircraft and B-1 bombers, alongside Tomahawk missiles deployed from US naval vessels: for discussion see Scharf (n 32) 9. For updated numbers, see Global Conflict Tracker, Council of Foreign Relations, https://www.cfr.org/nteractives/global-conflict-tracker#!/conflict/war-against-islamic-state-in-iraq; ‘Islamic State and the Crisis in Iraq and Syria in Maps’, BBC News, 28 March 2018, https://www.bbc.com/news/world-middle-east-27838034.

¹¹⁷ UNSC, Identical letters dated 17 September 2015 (n 108); UNSC, Identical letters dated 18 September 2015 (n 108); Jackson (n 6) 157; Goodman (n 108); Ryan Goodman, ‘Assad: Willing to Risk Direct Confrontation with U.S. over Moderate Rebels – and Stronger Opposition to US Airstrikes’, Just Security, 27 January 2015, http://justsecurity.org/19419/syria-assad-risk-directconfrontation-moderate-rebels-opposition-airstrikes; Smith (n 90).

¹¹⁸ Jones and others (n 8).

¹¹⁹ This occurred mainly because of the territorial losses, bringing about a dramatic reduction of 80% from 2015 to 2017 in its average monthly revenue: see Jackson (n 6) 142. For elaboration see Stefan Heissner and others, ‘Caliphate in Decline: An Estimate of Islamic State's Financial Fortunes’ (2017) Report of The International Centre for the Study of Radicalisation, http://icsr.info/wp-content/uploads/2017/02/ICSR-Report-Caliphate-in-Decline-An-Estimate-of-Islamic-States-Financial-Fortunes.pdf.

¹²⁰ Coker, Schmitt and Callimachi (n 9).

¹²¹ Emma Graham-Harrison, ‘Iraq Formally Declares End to Fight against Islamic State’, The Guardian, 9 December 2017, https://www.theguardian.com/world/2017/dec/09/iraq-formally-declares-end-to-fight-against-islamic-state; Babak Dehghanpisheh, ‘Iran's President Declares End of Islamic State’, Reuters, 21 November 2017, https://www.reuters.com/article/us-mideast-crisis-rouhani-islamic-state/irans-president-declares-end-of-islamic-state-idUSKBN1DL0J5; Alec Luhn, ‘Russia Declares “Mission Accomplished” against Islamic State in Syria’, The Telegraph, 7 December 2017, http://www.telegraph.co.uk/news/2017/12/07/russia-declares-mission-accomplished-against-islamic-state-syria.

¹²² ‘US-Led Coalition Strikes Kill 150 Islamic State Militants in Syria’, The Guardian, 24 January 2018, https://www.theguardian.com/us-news/2018/jan/24/us-led-coalition-strikes-kill-150-islamic-state-militants-in-syria.

¹²³ Eric Schmitt and others, ‘Its Territory May Be Gone, but the U.S. Fight Against ISIS Is Far From Over’, New York Times, 24 March 2019, https://www.nytimes.com/2019/03/24/us/politics/us-isis-fight.html?rref=collection%2Ftimestopic%2FIslamic%20State%20in%20Iraq%20and%20Syria%20(ISIS). See also Coker, Schmitt and Callimachi (n 9).

¹²⁴ Wu, Watkins and Callimachi (n 10).

¹²⁵ Martin Chulov, ‘Nowhere Left to Run: How the US Finally Caught Up with ISIS Leader Baghdadi’, The Guardian, 27 October 2019, https://www.theguardian.com/world/2019/oct/27/nowhere-left-to-run-how-the-us-finally-caught-up-with-isis-leader-baghdadi.

¹²⁶ McCants (n 3) 140. See also Warrick (n 86); William McCants and Craig Whiteside, ‘The Islamic State's Coming Rural Revival’, Brookings, 25 October 2016, https://www.brookings.edu/blog/markaz/2016/10/25/the-islamic-states-coming-rural-revival.

¹²⁷ For example, the Australian Attorney General referred to the possibility that the Islamic State might seek to establish a caliphate in Indonesia: Adam Brereton, ‘ISIS Seeking to Set Up “Distant Caliphate” in Indonesia, George Brandis Warns’, The Guardian, 21 December 2015, https://www.theguardian.com/world/2015/dec/22/isis-seeking-to-set-up-distant-caliphate-in-indonesia-george-brandis-wams. Another possible effect of the Islamic State is that the resurgence of the idea of a caliphate will have spillover effects for the evolution of radical Islamic movements across the Muslim world: for discussion see Bar, Shmuel, ‘The Implications of the Caliphate’ (2016) 35 Comparative Strategy 1, 8CrossRefGoogle Scholar.

¹²⁸ When American-led forces withdrew from Iraq in 2011 it was estimated that the Islamic State's predecessor, the Islamic State of Iraq, was down to a few hundred soldiers. Within three years, however, the group of diminished insurgents was able to regroup and roar across Iraq and Syria, declaring an Islamic caliphate from the Mediterranean coast of Syria almost to the Iraqi capital, Baghdad: see Coker, Schmitt and Callimachi (n 9); Kadercan (n 2) 64–67.

¹²⁹ Foreign fighters can move around on their passports for as long as no personal sanctions exist against them; other fighters have also tried to use the wave of refugees from Syria and Iraq into Europe and enter under the pretence of escaping from the hostilities: for discussion see McCabe, Thomas R, ‘Jihad in the West: Are Returning Jihadists a Major Threat?’ (2017) 24 Middle East Quarterly 1, 2Google Scholar.

¹³⁰ Coker, Schmitt and Callimachi (n 9).

¹³¹ Another danger arises from cases involving ‘lone wolf’ assaults, which are inspired or enabled by Islamic State propaganda online: for discussion of the phenomenon see Hamoudi, Haider Ala, ‘“Lone Wolf” Terrorism and the Classical Jihad: On the Contingencies of Violent Islamic Extremism’ (2015) 11 Florida International University Law Review 19Google Scholar; Tsesis, Alexander, ‘Social Media Accountability for Terrorist Propaganda’ (2017) 86 Fordham Law Review 605Google Scholar.

¹³² Syria and Russia released statements opposing the US campaign in Syria, calling it an act of aggression: see Jackson (n 6) 135; UNSC, Identical letters dated 17 September 2015 (n 108); UNSC, Identical letters dated 18 September 2015 (n 108); Goodman (n 108); Goodman (n 117); Smith (n 90).

¹³³ UNSC, Letter dated 15 October 2015 (n 103); for elaboration see Kajtar (n 3) 556.

¹³⁴ UNSC, Letter dated 10 December 2015 from the Chargé d'Affaires a.i. of the Permanent Mission of Germany to the United Nations addressed to the President of the Security Council (10 December 2015), UN Doc S/2015/946 (‘ISIL has carried out, and continues to carry out, armed attacks against Iraq, France, and other States … States that have been subjected to armed attack by ISIL originating in this part of Syrian territory are therefore justified under Article 51 of the Charter of the United Nations to take necessary measures of self-defence, even without the consent of the Government of the Syrian Arab Republic. Exercising the right of collective self-defence, Germany will now support the military measures of those States that have been subjected to attacks by ISIL’); UNSC, Letter dated 7 June 2016 from the Permanent Representative of Belgium to the United Nations addressed to the President of the Security Council (9 June 2016), UN Doc S/2016/523 (‘the Kingdom of Belgium is taking necessary and proportionate measures against the terrorist organization “Islamic State in Iraq and the Levant” (ISIL, also known as Da'esh) in Syria in the exercise of the right of collective self-defence, in response to the request from the Government of Iraq … In the light of this exceptional situation, States that have been subjected to armed attack by ISIL originating in that part of the Syrian territory are therefore justified under Article 51 of the Charter to take necessary measures of self-defence. Exercising the right of collective self-defence, Belgium will support the military measures of those States that have been subjected to attacks by ISIL. Those measures are directed against the so-called “Islamic State in Iraq and the Levant” and not against the Syrian Arab Republic’).

¹³⁵ Nicaragua v US (n 21) [95];

¹³⁶ Legal Consequences of the Construction of a Wall (n 17) separate opinion of Judge Elaraby, [139]; Democratic Republic of the Congo v Uganda (n 29) [146]–[147].

¹³⁷ UNSC, Letter dated 7 September 2015 from the Permanent Representative of the United Kingdom of Great Britain and Northern Ireland to the United Nations addressed to the President of the Security Council (26 November 2014), UN Doc S/2014/851 (‘I am writing in accordance with Article 51 of the Charter of the United Nations to report to the Security Council that the United Kingdom of Great Britain and Northern Ireland is taking measures in support of the collective self-defence of Iraq as part of international efforts led by the United States. These measures are in response to the request by the Government of Iraq for assistance in confronting the attack by the Islamic State in Iraq and the Levant (ISIL) on Iraq’).

¹³⁸ The UK also mentions in a third letter sent to the Security Council that its use of force is applied as called for by the Security Council in its Resolution 2249 (n 4) but, as will be discussed in the next chapter, reliance on Security Council authorisation relating to the Islamic State seems as problematic as the other justifications raised by the UK: for further discussion see the next section of this article. For the UK justification see UNSC, Letter dated 7 September 2015, ibid; Arabella Lang, ‘Legal Basis for UK Military Action in Syria’ (2015) HC Library Briefing Paper No. 7404, http://researchbriefings.parliament.uk/ResearchBriefing/Summary/CBP-7404#fullreport.

¹³⁹ Reisman, W Michael and Armstrong, Andrea, ‘The Past and Future of the Claim of Preemptive Self-Defense’ (2006) 100(3) American Journal of International Law 525CrossRefGoogle Scholar.

¹⁴⁰ Monica Hakimi, ‘The UK's Most Recent Volley on Defensive Force’, EJIL: Talk!, 12 January 2017, https://www.ejiltalk.org/the-uks-most-recent-volley-on-defensive-force. As noted by Hakimi, under the ‘accumulation of events’ theory, multiple small-scale attacks can be considered collectively as creating the right to respond with defensive force.

¹⁴¹ Scharf (n 32) 23.

¹⁴² The military coalitions enjoyed significant support, but some states did not support them. In particular, Russia was not willing to support any operations without authorisation, and additional criticism was raised by Argentina, Chad, Ecuador, Iran and Venezuela: for discussion see Starski (n 7) 488; Corten, Olivier, ‘The “Unwilling or Unable” Test: Has It Been, and Could It Be, Accepted?’ (2016) 29 Leiden Journal of International Law 777, 789CrossRefGoogle Scholar.

¹⁴³ For example, the Syrian government used chemical agents against its population twice, once in 2017 and once in 2018: for discussion see Mary Ellen O'Connell, ‘Unlawful Reprisals to the Rescue against Chemical Attacks?’, EJIL: Talk!, 12 April 2018, https://www.ejiltalk.org/unlawful-reprisals-to-the-rescue-against-chemical-attacks; Monica Hakimi, ‘The Attack on Syria and the Contemporary Jus ad Bellum’, EJIL: Talk!, 15 April 2018, https://www.ejiltalk.org/the-attack-on-syria-and-the-contemporary-jus-ad-bellum.

¹⁴⁴ Examples include the right of hot pursuit and collective self-defence alongside Iraq. At the domestic level, the US affiliated the Islamic State with Al Qaeda in order to rely on the existing authorisation to use military force against the latter following the attacks on 11 September 2001: see UNSC, Letter dated 23 September 2014 (n 11). For discussion see Marko Milanovic, ‘Belgium's Article 51 Letter to the Security Council’, EJIL: Talk!, 17 June 2016, http://www.ejiltalk.org/belgiums-article-51-letter-to-the-security-council. For discussion see Scharf (n 32) 49.

¹⁴⁵ UNSC, Letter dated 23 September 2014 (n 11) (‘ISIL and other terrorist groups in Syria are a threat not only to Iraq, but also to many other countries, including the US and our partners in the region and beyond. States must be able to defend themselves, in accordance with the inherent right of individual and collective self-defence, as reflected in Article 51 of the Charter of the United Nations, when, as is the case here, the government of the State where the threat is located is unwilling or unable to prevent the use of its territory for such attacks. The Syrian regime has shown that it cannot and will not confront these safe havens effectively itself’).

¹⁴⁶ For discussion see Acharya, Upendra D, ‘International Lawlessness, International Politics and the Problem of Terrorism: A Conundrum of International Law and U.S. Foreign Policy’ (2012) 40 Denver Journal of International Law and Policy 144Google Scholar; Lustick, Ian S, ‘Fractured Fairy Tale: The War on Terror and the Emperor's New Clothes’ (2007) 16 Minnesota Journal of International Law 335Google Scholar; Gathii, James Thuo, ‘Failing Failed States: A Response to John Yoo’ (2011) 2 California Law Review Circuit 40Google Scholar; Lorca, Arnulf Becker, ‘Rules for the “Global War On Terror”: Implying Consent and Presuming Conditions for Intervention’ (2012) 45 New York University Journal of International Law and Politics 1Google Scholar.

¹⁴⁷ Scharf (n 32) 49; Vogel, Ryan J, ‘Drone Warfare and the Law of Armed Conflict’ (2010) 39 Denver Journal of International Law and Policy 101, 131Google Scholar; Larson, Kurt and Malamud, Zachary, ‘The United States, Pakistan, the Law of War and the Legality of the Drone Attacks’ (2011) 10 Journal of International Business & Law 1, 20Google Scholar; Starski (n 7) 457. Part of the justification for the use of force in states like Yemen was that they were ‘lawless areas’: for discussion see Bennett, Joshua, ‘Exploring the Legal and Moral Bases for Conducting Targeted Strikes Outside of the Defined Combat Zone’ (2012) 26 Notre Dame Journal of Law, Ethics & Public Policy 549Google Scholar.

¹⁴⁸ UNSC, Letter dated 9 September 2015 (n 13).

¹⁴⁹ UNSC, Letter dated 31 March 2015 (n 14).

¹⁵⁰ Green (n 12).

¹⁵¹ UNSC, Letter dated 24 July 2015 (n 15).

¹⁵² eg, Deeks, Ashley, ‘“Unwilling or Unable”: Toward a Normative Framework for Extraterritorial Self-Defense’ (2012) 52 Virginia Journal of International Law 483Google Scholar; Christof Heyns, Report of the Special Rapporteur on Extrajudicial, Summary or Arbitrary Executions (13 September 2013), UN Doc A/68/382, para 91; James Crawford, ‘Sovereignty as a Legal Value’ in Crawford and Koskenniemi (n 16) 127; Nyamuya Maogoto, ‘Somaliland: Scrambled by International Law?’ in French (n 16) 220.

¹⁵³ Duffy, Helen, The ‘War on Terror’ and the Framework of International Law (2nd edn, Cambridge University Press 2015) 291–92CrossRefGoogle Scholar. For discussion of the manner in which the actions against the Islamic State affected this doctrine see Scharf (n 32) 49; for a different view see Corten (n 142) 777. For discussion of the application of this doctrine relating to Syria see van der Vyver, Johan D, ‘The ISIS Crisis and the Development of International Humanitarian Law’ (2016) 30 Emory International Law Review 532, 557Google Scholar.

¹⁵⁴ Maogoto (n 152) 220. For criticism see Gathii (n 146) 44.

¹⁵⁵ Lorca (n 146) 44.

¹⁵⁶ Convention on the Rights and Duties of States (entered into force 26 December 1934) 165 LNTS 19, art 8.

¹⁵⁷ Lorca, Arnulf Becker, ‘Sovereignty Beyond the West: The End of Classical International Law’ (2011) 13 Journal of the History of International Law 7, 67CrossRefGoogle Scholar.

¹⁵⁸ Gathii (n 146) 48.

¹⁵⁹ Mehta went further and contended that Western states feel an internal urge to disrespect international law when it comes to non-Western states: Mehta, Uday Singh, Liberalism and Empire: A Study in Nineteenth-Century British Liberal Thought (University of Chicago Press 1999) 20CrossRefGoogle Scholar.

¹⁶⁰ Schill, Stephan W, ‘Lex Mercatoria’ in Wolfrum, Rüdiger (ed), The Max Planck Encyclopedia of Public International Law (Oxford Public International Law 2014)Google Scholar, https://opil.ouplaw.com/view/10.1093/law:epil/9780199231690/law-9780199231690-e1534.

¹⁶¹ Di Robilant, Anna, ‘Genealogies of Soft Law’ (2006) 54 American Journal of Comparative Law 499, 512CrossRefGoogle Scholar.

¹⁶² Alton, Richard AC, ‘An Examination of Historical Reconstruction's Impact on Modern Customary International Law via an Analysis of Medieval Post-Conflict Ransoming of Prisoners’ (2016) 39 Suffolk Transnational Law Review 271, 276Google Scholar.

¹⁶³ Qureshi, Waseem Ahmad, ‘Examining the Legitimacy and Reasonableness of the Use of Force: From Just War Doctrine to the Unwilling-or-Unable Test’ (2018) 42(3) Oklahoma City University Law Review 221, 235Google Scholar. The chivalric code distinguished between innocents and combatants, and later influenced scholars such as Grotius in their conceptions of non-combatants. See also Mcelroy, Robert W, Morality and American Foreign Policy (Princeton University Press 1992) 150CrossRefGoogle Scholar.

¹⁶⁴ This system, similar to the chivalric code, was implemented through special, often temporary, merchant courts: for discussion see Schill (n 160); for discussion in the imperial context see Whitman, James Q, ‘Western Legal Imperialism: Thinking about the Deep Historical Roots’ (2009) 10 Theoretical Inquiries in Law 305, 322CrossRefGoogle Scholar.

¹⁶⁵ Seth Lazar, ‘War’ in Edward N Zalta (ed), Stanford Encyclopedia of Philosophy, 3 May 2016, https://plato.stanford.edu/entries/war/#LegiAuth.

¹⁶⁶ Qureshi (n 163) 227; see also Fabre, Cécile, Cosmopolitan War (Oxford University Press 2012) 142CrossRefGoogle Scholar.

¹⁶⁷ Corten (n 142) 797.

¹⁶⁸ Scharf (n 32) 49; see also Gregory M Travalio, ‘Terrorism, International Law, and the Use of Military Force’ (2000) 18 Wisconsin International Law Journal 145.

¹⁶⁹ This rationale is similar to that laid down relating to the doctrine of R2P, discussed at Section 5 of this article, according to which if a certain state is unable or unwilling to stop mass atrocities from occurring on its territory, other states have a collective and subsidiary responsibility to take measures to protect the civilian population. R2P is subject to several criteria: seriousness of the harm; just cause for intervention; intervention as a last resort; proportionality; and an assessment of consequences: see Amir Seyedfarshi, ‘French Interventionism in the Age of R2P: A Critical Examination of the Case of Mali’ (2016) 7 Creighton International and Comparative Law Journal 2, 21; Lekas (n 35) 343. See further Spencer Zifcak, ‘The Responsibility to Protect’ in Evans (n 17) 505.

¹⁷⁰ Scharf (n 32) 49.

¹⁷¹ This term was coined by Professor Richard Falk in 1985, and has been used by several others in order to symbolise the advent of the modern international legal regime: see Falk, Richard and others (eds), The Grotian Moment in International Law: A Contemporary Perspective (Westview Press 1985) 7Google Scholar. For other examples see Scharf, Michael P, Customary International Law in Times of Fundamental Change: Recognizing Grotian Moments (Cambridge University Press 2013)CrossRefGoogle Scholar; Michael P Scharf, ‘Seizing the “Grotian Moment”: Accelerated Formation of Customary International Law in Times of Fundamental Change’ (2010) 43 Cornell International Law Journal 429 (discussing the evolution brought about by the Nuremberg Charter and rulings); UNSC, An Agenda for Peace: Preventive Diplomacy, Peacemaking, and Peace-Keeping, Report of the Secretary-General (17 June 1992), UN Doc A/47/277-S/24111, para 17.

¹⁷² Scharf (n 32). In his view, as reflected in the practice of international bodies like the Organization of American States and the North Atlantic Treaty Organization, these attacks changed the perception that terrorists are always dependent on state funding, as more and more groups were able to grow and expand in the territories of failed states, and that only states can commit an armed attack giving rise to a right of counter self-defence. As for the international response, see UNSC Res 2170 (n 4); UNSC Res 1373 (n 63). Scharf also refers to the fact that several states – such as Colombia, Ethiopia, Kenya, Russia and Turkey – relied on the response to the 11 September attacks when they engaged in warfare against NSAs.

¹⁷³ UNSC Res 2249 (n 4). For discussion see Milanovic (n 110); Weller (n 110). For elaboration see Yourish and others (n 111); Kadercan (n 2) 64.

¹⁷⁴ Corten (n 142) 780–83.

¹⁷⁵ Qureshi, Waseem Ahmad, ‘International Law and the Application of the Unwilling or Unable Test in the Syrian Conflict’ (2018) 11 Drexel Law Review 62, 88Google Scholar; Corten (n 142) 780–83.

¹⁷⁶ Tsagourias, Nicholas, ‘Self-Defence against Non-State Actors: The Interaction between Self-Defence as a Primary Rule and Self-Defence as a Secondary Rule’ (2016) 29 Leiden Journal of International Law 801CrossRefGoogle Scholar; Kajtar (n 3) 574.

¹⁷⁷ Corten (n 142) 780–83. For discussion of the elements required for the development of custom in international law see Schachter, Oscar, ‘Entangled Treaty and Custom’ in Dinstein, Yoram and Tabory, Mala (eds), International Law at a Time of Perplexity: Essays in Honour of Shabtai Rosenne (Martinus Nijhoff 1989) 717, 730Google Scholar; Barboza, Julio, ‘The Customary Rule: From Chrysalis to Butterfly’ in Barea, Calixto A Armas and others (eds), Liber Amicorum ‘In Memoriam’ of Judge José María Ruda (Martinus Nijhoff 2000) 1, 6Google Scholar; Pomson, Ori, ‘Does the Monetary Gold Principle Apply to International Courts and Tribunals Generally?’ (2019) 10 Journal of International Dispute Settlement 88, 120–21CrossRefGoogle Scholar.

¹⁷⁸ Kajtar (n 3) 574.

¹⁷⁹ Corten (n 142) 780–83.

¹⁸⁰ Peters (n 66).

¹⁸¹ Acharya (n 146) 144.

¹⁸² Lustick (n 146).

¹⁸³ Hassan (n 5); Al-Ibrahim (n 93).

¹⁸⁴ For discussion of the secular basis of the current international order see Lilla (n 95) 7.

¹⁸⁵ Delahunty (n 89) 36.

¹⁸⁶ Corten (n 142) 797.

¹⁸⁷ Tsagourias (n 176) 810.

¹⁸⁸ UNSC, Letter dated 23 September 2014 (n 11).

¹⁸⁹ Green (n 12).

¹⁹⁰ UNSC, Letter dated 9 September 2015 (n 13).

¹⁹¹ UNSC, Letter dated 31 March 2015 (n 14).

¹⁹² UNSC, Letter dated 24 July 2015 (n 15).

¹⁹³ See the list of NSAs at n 104.

¹⁹⁴ For discussion see Kajtar (n 3) 540.

¹⁹⁵ Zachary Laub, ‘Syria's War: The Descent into Horror’, Council on Foreign Relations, 23 October 2019, https://www.cfr.org/interactives/syrias-civil-war-descent-into-horror#!/syrias-civil-war-descent-into-horror.

¹⁹⁶ UNSC, Identical letters dated 17 September 2015 (n 108); UNSC, Identical letters dated 18 September 2015 (n 108).

¹⁹⁷ UNSC Res 2170 (n 4); UNSC Res 2249 (n 4).

¹⁹⁸ UNSC, Identical letters dated 14 October 2015 from the Permanent Representative of the Syrian Arab Republic to the United Nations addressed to the Secretary-General and the President of the Security Council (16 October 2015), UN Doc S/2015/789.

¹⁹⁹ UNSC, Letter dated 23 September 2014 (n 11).

²⁰⁰ Green (n 12).

²⁰¹ UNSC, Letter dated 9 September 2015 (n 13).

²⁰² UNSC, Letter dated 31 March 2015 (n 14).

²⁰³ UNSC, Letter dated 24 July 2015 (n 15).

²⁰⁴ UNSC, Letter dated 18 June 2014 from the Permanent Representative of the Syrian Arab Republic to the United Nations addressed to the Secretary-General (4 January 2016), UN Doc S/2015/1048.

²⁰⁵ ibid.

²⁰⁶ Deeks (n 152) 520; for a similar view see Starski (n 7) 460.

²⁰⁷ Koskenniemi, Martti, The Politics of International Law (Hart 2011) 46Google Scholar.

²⁰⁸ ibid 39. In Koskenniemi's view, concreteness results from liberal principles and subjectivity of value, and it prescribes significance to state practice as a tangible verification tool in recognising the will and interests of states. Normativity requires application of the law regardless of the political differences of legal subjects and, in particular, states. For example, in the context of statehood and the need for recognition, those who advocate the declarative approach seek to rely on pure facts (and, most importantly, effective establishment of authority – effectivités), while those who support the constitutive approach argue in terms of a criterion external to facts (in particular, general recognition).

²⁰⁹ UNSC, Identical letters dated 17 September 2015 (n 108); UNSC, Identical letters dated 18 September 2015 (n 108).

²¹⁰ UNSC, Letter dated 10 December 2015 (n 134); UNSC, Letter dated 7 September 2015 (n 137); UNSC, Letter dated 23 September 2014 (n 11). For an illustrative discussion of the views of the members of the coalition see Longo (n 59) 908.

²¹¹ For discussion in the context of the Israeli occupation over Palestinian territories see Shany, Yuval, ‘Faraway, So Close: The Legal Status of Gaza After Israel's Disengagement’ (2005) 8 Yearbook of International Humanitarian Law 369CrossRefGoogle Scholar; Shany, Yuval, ‘Forty Years After 1967: Reappraising the Role and Limits of the Legal Discourse on Occupation in the Israeli-Palestinian Context: Binary Law Meets Complex Reality: The Occupation of Gaza Debate’ (2008) 41 Israel Law Review 68Google Scholar; Shany, Yuval, ‘The Law Applicable to Non-Occupied Gaza: A Comment on Bassiouni v Prime Minster of Israel’ (2009) 42 Israel Law Review 101CrossRefGoogle Scholar.

²¹² In the context of sovereignty and military occupation see Gross, Aeyal, The Writing on the Wall: Rethinking the International Law of Occupation (Cambridge University Press 2017) 56.CrossRefGoogle Scholar

²¹³ Gowlland-Debbas, Vera, ‘Note on the Legal Effects of Palestine's Declaration under Article 12(3) of the ICC Statute’ in Meloni, Chantal and Tognoni, Gianni (eds), Is There a Court for Gaza? A Test Bench for International Justice (TMC Asser Press 2012) 513Google Scholar; Shany, Yuval, ‘In Defence of Functional Interpretation of Article 12(3) of the Rome Statute: A Response to Yaël Ronen’ (2010) 8 Journal of International Criminal Justice 329, 334–35CrossRefGoogle Scholar; Anthea Roberts and Sandesh Sivakumaran, ‘Lawmaking by Nonstate Actors: Engaging Armed Groups in the Creation of International Humanitarian Law’ (2011) 37 Yale Journal of International Law 107, 120; Gross (n 212).

²¹⁴ In the ICC, for example, art 26 of the Rome Statute (n 73) dictates that jurisdiction is excluded over persons aged under 18. For additional examples see Shany (2008) (n 211) 73.

²¹⁵ A significant question is whether a person, when captured, should be qualified as a prisoner of war, which would give immunity from criminal prosecution. For discussion, especially in the context of an NSA such as the Islamic State, see Callen, Jason, ‘Unlawful Combatants and the Geneva Conventions’ (2004) 44 Virginia Journal of International Law 1025Google Scholar; Dörmann, Knut, ‘The Legal Situation of “Unlawful/Unprivileged Combatants”’ (2003) 85 International Review of the Red Cross 849Google Scholar; Shany, Yuval, ‘Human Rights and Humanitarian Law as Competing Legal Paradigms for Fighting Terror’ in Ben-Naftali, Orna (ed), International Humanitarian Law and International Human Rights Law: Pas de Deux (Oxford University Press 2011 ) 13Google Scholar. For a critical view of the rigidness of the regime see Elizabeth Holland, ‘The Qualification Framework of International Humanitarian Law: Too Rigid to Accommodate Contemporary Conflicts?’ (2011) 34 Suffolk Transnational Law Review 145.

²¹⁶ Scharf (n 32) 22.

²¹⁷ Accordance with International Law of the Unilateral Declaration of Independence in respect of Kosovo (n 61) [80].

²¹⁸ Legal Consequences of the Construction of a Wall (n 17) separate opinion of Judge Elaraby, [139]; Armed Activities on the Territory of the Congo (n 29) [146]–[147].

²¹⁹ Shany (2008) (n 211) 73. Also see Clarke, Jessica A, ‘Adverse Possession of Identity: Radical Theory, Conventional Practice’ (2005) 84 Oregon Law Review 563, 600Google Scholar.

²²⁰ Gowlland-Debbas (n 213) 513; Shany (n 213) 334; Roberts and Sivakumaran (n 213).

²²¹ For discussion see Gross (n 212).

²²² EECC Partial Award, Western Front, Aerial Bombardment and Related Claims, Eritrea's Claims, XXVI RIAA 291 (2005).

²²³ Gross (n 212) 7.

²²⁴ Aeyal Gross, ‘Rethinking Occupation: The Functional Approach’, Opinio Juris, 23 April 2012, http://opiniojuris.org/2012/04/23/rethinking-occupation-the-functional-approach/.

²²⁵ Gross (n 212) 77.

²²⁶ ICTY, Prosecutor v Mladen Naletilic, IT-98-34-T 203-08, 31 March 2003. For discussion of the case see Gross (n 212) 64–47.

²²⁷ ICRC, Commentary on the First Geneva Convention: Convention (I) for the Amelioration of the Condition of the Wounded and Sick in Armed Forces in the Field (ICRC and Cambridge University Press 2016) Article 2, para 310, https://ihl-databases.icrc.org/applic/ihl/ihl.nsf/Comment.xsp?action=openDocument&documentId=BE2D518CF5DE54EAC1257F7D0036B518#64_B.

²²⁸ Quasi-states are political entities with significant state-like features. Another parallel term occasionally used is ‘de facto states’ or ‘de facto regimes’. For discussion see Sterio, Milena, ‘A Grotian Moment: Changes in the Legal Theory of Statehood’ (2011) 39 Denver Journal of International Law and Policy 209Google Scholar; Essen, Jonte van, ‘De Facto Regimes in International Law’ (2012) 28 Utrecht Journal of International and European Law 31CrossRefGoogle Scholar.

²²⁹ For discussion relating to governance at the international level see Rosenau, James, Along the Domestic-Foreign Frontier: Exploring Governance in a Turbulent World (Cambridge University Press 1997) 80CrossRefGoogle Scholar; Held, David, Democracy and the Global Order: From the Modern State to Cosmopolitan Governance (Stanford University Press 1995)Google Scholar.

²³⁰ Convention on the Rights and Duties of States (n 156) art 1. For discussion of the classical notion of statehood see Crawford, James, The Creation of States in International Law (2nd edn, Oxford University Press 2006) 46Google Scholar; Jennings and Watts (n 53) 717–18; Higgins, Rosalyn, The Development of International Law through the Political Organs of the United Nations (Oxford University Press 1963) 25Google Scholar.

²³¹ Risse, Thomas, ‘Governance under Limited Sovereignty’ in Finnemore, Martha and Goldstein, Judith (eds), Back to Basics: State Power in a Contemporary World (Oxford University Press 2013) 78Google Scholar. An example in the context of failing to meet the territory demand is the Czech Republic: see Acquaviva, Guido, ‘Subjects of International Law: A Power-Based Analysis’ (2005) 38 Vanderbilt Journal of Transnational Law 345, 394Google Scholar. For discussion of the two components of statehood in this regard – authority and effective control – see Krasner, Stephen D, Sovereignty: Organized Hypocrisy (Princeton University Press 1999) 4CrossRefGoogle Scholar.

²³² Shany (n 213) 334. See also William Thomas Worster, ‘Law, Politics, and the Conception of the State in State Recognition Theory’ (2009) 27 Boston University International Law Journal 115. With regard to Palestine see Michael G Kearney, ‘Why Statehood Now: A Reflection on the ICC's Impact on Palestine's Engagement with International Law’ in Meloni and Tognoni (n 213) 391. For example, when Palestine declared that it accepts the jurisdiction of the International Criminal Court (ICC), first in 2009 and later again in 2015, the ICC prosecutor faced the dilemma of whether to treat Palestine as a state for the purposes of the Rome Statute establishing the ICC (n 73): for discussion see Amichai Cohen and Tal Mimran, ‘The Palestinian Authority and the International Criminal Court’, The Israel Democracy Institute, 10 February 2015, https://en.idi.org.il/articles/5216. In the view of Shany, as the main goal of the Rome Statute is to end impunity through the exercise of complementary international jurisdiction by the ICC, then acceptance of its declaration will promote the main goal of the ICC by exercising jurisdiction over a situation where serious crimes may have occurred (the Israeli-Palestinian conflict) and prevent the option of a legal black hole (territories over which no state exercises sovereignty).

²³³ Gowlland-Debbas (n 213) 513.

²³⁴ Shany (n 213) 334; Roberts and Sivakumaran (n 213) 120. For additional discussion relating to Taiwan see Jure Vidmar, ‘States, Governments, and Collective Recognition’ (2017) 31 Chinese (Taiwan) Yearbook of International Law and Affairs 136; Beat Dold, ‘Concepts and Practicalities of the Recognition of States’ (2012) 22 Swiss Review of International and European Law 81, 88.

²³⁵ For illustration of the problem of binary application of occupation law in the context of the Gaza Strip see Shany (2008) (n 211).

²³⁶ ICTY, Prosecutor v Tadić, Appeal on Jurisdiction, IT-94-1-AR72, 2 October 1995, [70]. For elaboration see Shany (n 215); Milanovic, Marko, ‘Lessons for Human Rights and Humanitarian Law in the War on Terror: Comparing Hamdan and the Israeli Targeted Killings Case’ (2007) 866 International Review of the Red Cross 373Google Scholar.

²³⁷ Essen (n 228) 34.

²³⁸ Gross (n 212) 8.

²³⁹ For discussion relating to governance at the international level see Rosenau (n 229); Held (n 229).

²⁴⁰ Convention on the Rights and Duties of States (n 156) art 1. For discussion of the classical notion of statehood see Crawford (n 230) 46; Jennings and Watts (n 53) 717–18; Higgins (n 230) 25.

²⁴¹ An example in the context of failing to meet the territory demand is the Czech Republic: see Acquaviva (n 231) 394.

²⁴² Shany (n 213) 334; see also Worster (n 232).

²⁴³ Longo (n 59) 896.

²⁴⁴ UN Charter (n 18) 2 para 7; Nicaragua v US (n 21) [202]; Kelly (n 21) 392. See also Island of Palmas Case (n 16) 829–71; SS ‘Lotus’ (France v Turkey) (n 21); Brand (n 21) 1686; Mégret (n 16); Cohan (n 21).

²⁴⁵ Grim (n 22) 1043; Tsagourias (n 22) 326.

²⁴⁶ For discussion of this rationale see Charles de Visscher, Les Effectivités du Droit International Public (Éditions A Pedone 1967); Christakis, Theodore and Constantinides, Aristoteles, ‘Territorial Disputes in the Context of Secessionist Conflicts’ in Kohen, Marcelo G and Hébié, Mamadou (eds), Research Handbook on Territorial Disputes in International Law (Edward Elgar 2017) 343Google Scholar.

²⁴⁷ Bhuta, Nehal, ‘The Role International Actors other than States Can Play in the New World Order’ in Cassese, Antonio (ed), Realizing Utopia: The Future of International Law (Oxford University Press 2012) 70Google Scholar.

²⁴⁸ Salvatore Zappalà, ‘Can Legality Trump Effectiveness in Today's International Law?’ in Cassese, ibid 106.

²⁴⁹ Acts that are in contravention of peremptory norms are invalid ab initio, and this principle seeks to uphold the illegality and invalidity of the alleged territorial regime. For discussion of the transition from illegal regimes into states see Ronen, Yaël, Transition from Illegal Regimes under International Law (Cambridge University Press 2013)Google Scholar; Dugard, John, Recognition and the United Nations (Grotius Publications Ltd 1987) 49Google Scholar.

²⁵⁰ Gabčíkovo-Nagymaros Project (n 41) [133]; Factory at Chorzów (Germany v Poland) Jurisdiction (1925) PCIJ Rep (Ser A, No 9) 31.

²⁵¹ Lauterpacht, Hersch, Recognition in International Law (Cambridge University Press 1947) 402Google Scholar. The rule of non-recognition is based on the Stimson doctrine enunciated in 1932, during the Japanese invasion of Manchuria and in the international response to this act. It has been applied consistently by international tribunals, such as the ICJ: see, eg, Legal Consequences for States of the Continued Presence of South Africa in Namibia (South West Africa) notwithstanding Security Council Resolution 276 (1970), Advisory Opinion [1971] ICJ Rep 16, [124].

²⁵² Weller (n 110).

²⁵³ UNSC Res 82 (25 June 1950), UN Doc S/1501; UNSC Res 678 (29 November 1990), UN Doc S/RES/678.

²⁵⁴ UNSC Res 1373 (n 63).

²⁵⁵ UNSC Res 598 (20 July 1987), UN Doc S/RES/0598.

²⁵⁶ Henkin (n 60) 11.

²⁵⁷ Jessica Elbaz, ‘International Stalemate: The Need for a Structural Revamp of the U.N. Security Council’ (2016) 15 Cardozo Public Law, Policy, and Ethics Journal 211, 334. For further discussion see Amber Fitzgerald, ‘Security Council Reform: Creating a More Representative Body of the Entire U.N. Membership’ (2000) 12 Pace International Law Review 319; Arias, Inocencio, ‘Humanitarian Intervention: Could the Security Council Kill the United Nations?’ (2000) 23 Fordham International Law Journal 1005.Google Scholar

²⁵⁸ Scharf (n 32) 23.

²⁵⁹ UNSC Res 2170 (n 4); Lekas (n 35) 324.

²⁶⁰ UNSC Res 2170 (n 4) para 19; Longo (n 59) 903. For later sanctions imposed by the Security Council see UNSC Res 2253 (17 December 2015), UN Doc S/RES/2253. For discussion of Security Council measures and human rights obligations in international law see Tzanakopoulos, Antonios, ‘Collective Security and Human Rights’ in de Wet, Erika and Vidmar, Jure (eds), Hierarchy in International Law: The Place of Human Rights (Oxford University Press 2010) 42Google Scholar.

²⁶¹ UNSC Res 2170 (n 4) para 9; Lekas (n 35) 324. Such domestic proceedings have begun recently, for example, in Germany (in the Higher Regional Court of Frankfurt).

²⁶² Scharf (n 32) 23.

²⁶³ For discussion see Fitzgerald (n 257); Arias (n 257); Zifcak (n 169) 504; Elbaz (n 257).

²⁶⁴ UNSC Res 2249 (n 4).

²⁶⁵ Weller (n 110).

²⁶⁶ UNSC, Letter dated 7 September 2015 (n 137) (‘Great Britain and Northern Ireland is taking necessary and proportionate measures against ISIL/Daesh in Syria, as called for by the Council in resolution 2249 (2015), in exercise of the inherent right of individual and collective self-defence’).

²⁶⁷ For discussion see Dapo Akande and Marko Milanovic, ‘The Constructive Ambiguity of the Security Council's ISIS Resolution’, EJIL: Talk!, 21 November 2015, http://www.ejiltalk.org/the-constructive-ambiguity-of-the-security-councils-isis-resolution. For a more expansive reading of the resolution see Weller (n 110). Controversies surrounding the interpretation of Security Council resolutions are not uncommon, as one can recall the controversy relating to the use of force by the US in Iraq during 2003. For discussion see Donald Nungesser, ‘United States’ Use of the Doctrine of Anticipatory Self-Defense in Iraqi Conflicts’ (2004) 16 Pace International Law Review 193; Jorge Alberto Ramirez, ‘Iraq War: Anticipatory Self-Defense or Unlawful Unilateralism?’ (2003) 34 California Western International Law Journal 1; Matthew D Campbell, ‘Bombs Over Baghdad: Addressing Criminal Liability of a U.S. President for Acts of War’ (2006) 5 Washington University Global Studies Law Review 235, 240; Lustick (n 146).

²⁶⁸ UN Security Council, Letter dated 18 June 2014 (n 204) para 6.

²⁶⁹ Kajtar (n 3) 570.

²⁷⁰ UN Charter (n 18) art 42.

²⁷¹ This demonstrates the systemic deficit that the right of veto brings about in the work of the Security Council: for discussion see Fitzgerald (n 257); Arias (n 257); Zifcak (n 169) 504; Elbaz (n 257).

²⁷² Kelly (n 21) 384; Longo (n 59) 898; UNSC Res 1973 (17 March 2011), UN Doc S/RES/1973. For discussion relating the development of the doctrine see Zifcak (n 169) 504.

²⁷³ Gerry Simpson, ‘International Law in Diplomatic History’ in Crawford and Koskenniemi (n 16) 43.

²⁷⁴ BS Chimni, ‘Legitimating the International Rule of Law’ in Crawford and Koskenniemi (n 16) 290, 300.

²⁷⁵ This concept is subject to several criteria: seriousness of the harm; just cause for intervention; intervention as a last resort; proportionality; and an assessment of consequences: see Seyedfarshi (n 169) 21; Lekas (n 35) 343; for more discussion see Zifcak (n 169) 505.

²⁷⁶ Lekas (n 35) 342.

²⁷⁷ UNSC Res 1973 (n 272).

²⁷⁸ Longo (n 59) 915.

²⁷⁹ Kelly (n 21) 385.

²⁸⁰ ‘UN Special Envoy for Syria Welcomes Ceasefire Understanding; Pledges UN Support’, UN News Centre, 9 September 2016, http://www.un.org/apps/news/story.asp?NewsID=54896#.WJpSJPl96Um.

²⁸¹ See, eg, UNSC Res 2165 (14 July 2014), UN Doc S/RES/2165.

²⁸² For discussion see Mary Ellen O'Connell, ‘Unlawful Reprisals to the Rescue against Chemical Attacks?’, EJIL: Talk!, 12 April 2018, https://www.ejiltalk.org/unlawful-reprisals-to-the-rescue-against-chemical-attacks; Hakimi (n 143).

²⁸³ Kelly (n 21) 385.

²⁸⁴ UNSC Res 1973 (n 272).

²⁸⁵ UNSC, Letter dated 9 September 2015 (n 13); UNSC, Letter dated 31 March 2015 (n 14); UNSC, Letter dated 24 July 2015 (n 15). For discussion see Green (n 12); Kelly (n 21) 391.

²⁸⁶ Crawford (n 152) 130.

²⁸⁷ Similarly, the ICC can initiate proceedings against a person only if there is no other state party to its Statute that is willing and able to prosecute that individual. In other words, the ICC can prosecute only when other states with jurisdiction fail to do so: Rome Statute (n 73) art 17. While this doctrine of complementarity demonstrates that the ICC is intended to supplement, rather than supplant national jurisdictions, it nevertheless indicates that when a state ‘fails’ in exercising its authority over its territory or nationals, its sovereignty is eroded in the sense that it may face military intervention or international criminal initiatives. Accordingly, the failure of Syria in exercising effective control over the territories held by several NSAs, and in particular the Islamic State, was invoked by Turkey and Germany as part of their legal justification for their use of force.

²⁸⁸ This is since sovereignty is a pillar in the international Westphalian legal system: see Koskenniemi (n 16) 11; Mégrét (n 16) 66.

²⁸⁹ Nicaragua v US (n 21) [249].

²⁹⁰ For discussion of the legal status of the doctrine see Zifcak (n 169) 504.

²⁹¹ Thomas Franck advanced the legitimacy theory, according to which these four elements create pressure towards compliance (as they are perceived to have come into being in accordance with the right process): determinacy, symbolic validation, coherence and adherence: for discussion see Franck, Thomas M, Fairness in International Law and Institutions (Oxford University Press 1995)Google Scholar. Generally speaking, legitimacy serves as an incentive to comply with international law, through the eyes of a rational decision maker that selects the course of action that maximises its utility: for discussion see Morrow, James, ‘A Rational Choice Approach to International Conflict’ in Geva, Nehemia and Mintz, Alex (eds), Decision Making on War and Peace: The Cognitive-Rational Debate (Lynne Reinner 1997) 11Google Scholar; Hirsch, Moshe, ‘Compliance with International Norms in the Age of Globalization: Two Theoretical Perspectives’ in Benvenisti, Eyal and Hirsch, Moshe (eds), The Impact of International Law on International Cooperation: Theoretical Perspectives (Cambridge University Press 2004) 166Google Scholar. For a realist view in relation to state adherence to international law (when the action correlates with the interests of the state) see Grieco, Joseph M, ‘Anarchy and the Limits of Cooperation: A Realist Critique of the Newest Liberal Institutionalism’ (1988) 42 International Organizations 485CrossRefGoogle Scholar.

²⁹² In fact, the Security Council was not able to adopt a resolution to authorise the use of force even after the use of chemical weapons by the Syrian regime, once in 2017 and also in 2018. In 2017 it was only the US who responded militarily by launching 59 Tomahawk missiles, and in 2018 the US was joined by the UK and France: see Hakimi (n 143). In both instances the US did not present any concrete legal arguments; rather, it presented political and moral considerations. Other states broadly expressed support for these attacks, given the gravity of the use of chemical weapons by the Syrian government, while ‘elegantly’ avoiding referring to the legality of the action. The UK was the only state to raise a legal claim, while France basically referred to the necessity of its response, invoking a language of reprisals, a regime which has long been out of date in international law. For discussion see Hakimi (n 140); Marko Milanovic, ‘The Syria Strikes: Still Clearly Illegal’, EJIL: Talk!, 15 April 2018, https://www.ejiltalk.org/the-syria-strikes-still-clearly-illegal; Alonso Gurmendi Dunkelberg and others, ‘Mapping States’ Reactions to the Syria Strikes of April 2018’, Just Security, 22 April 2018, https://www.justsecurity.org/55157/mapping-states-reactions-syria-strikes-april-2018. As for reprisals, their illegality has been affirmed by various UN institutions, ranging from the ICJ, the ILC and the General Assembly: Iran v US (n 38) separate opinion of Judge Simma, [12]; Legality of the Threat or Use of Nuclear Weapons, Advisory Opinion [1996] ICJ Rep 226.