What does it mean to say that international humanitarian law (IHL) strikes a realistic and meaningful balance between military necessity and humanity, and that the law therefore 'accounts for' military necessity? To what consequences does the law 'accounting for' military necessity give rise? Through real-life examples and careful analysis, this book challenges received wisdom on the subject by devising a new theory that not only reaffirms Kriegsräson's fallacy but also explains why IHL has no reason to restrict or prohibit militarily unnecessary conduct on that ground alone. Additionally, the theory hypothesises greater normative significance for humanitarian and chivalrous imperatives when they conflict with IHL rules. By combining international law, jurisprudence, military history, strategic studies, and moral philosophy, this book reveals how rational fighting relates to ethical fighting, how IHL incorporates contrasting values that shape its rules, and how law and theory adapt themselves to war's evolutions.

‘Military necessity is a notoriously difficult subject. It represents one side of the underlying principles of the law of armed conflict. Dr Hayashi engages in a nuanced discussion of the nature of the concept, and how it needs to be tempered by the principle of humanity that is its counterpoint. It is a work of great scholarship and a masterful approach to a deeply contentious area.’

Robert Cryer - University of Birmingham

‘Here, at last, our field gains a meticulous, comprehensive and novel examination of the law of war principle of military necessity. Dr Hayashi has delivered a supremely sophisticated and operationally informed study of the very heart of international regulation of the conduct of hostilities. This important text will be a commanding centrepiece of this subject and will inspire a generation of related scholarly commentary, juridical consideration and operational practice.’

Sean Watts - United States Military Academy at West Point, Lieber Institute for the Law of Land Warfare

‘During armed conflicts, acts of violence without military justification, as well as those that cause excessive collateral damage in relation to the expected military advantage, are prohibited by international humanitarian law. Military necessity is therefore at the heart of this law. Nobuo Hayashi has studied this essential question with such a depth of analysis and documentary richness that his book will certainly become indispensable for all those who apply, promote, teach, study and develop international humanitarian law.’

Yves Sandoz - University of Fribourg

‘Military necessity is an absolutely crucial, yet truly complex, concept with international humanitarian law and military ethics. How should we understand it? What trade-offs and dilemmas does it force us to face? And what do the law and actual cases tell us? Nobuo Hayashi gives us a detailed and authoritative overview that will be of great use not only to lawyers, but also to military practitioners and military ethicists.’

Henrik Syse - Peace Research Institute Oslo (PRIO), Bjørknes University College, and Chief Co-Editor of the Journal of Military Ethics