This Trialogue concerns the use of force in self-defence against non-State actors in the territory of third States under international law. International law relating to the use of force, in particular international law on the rules of self-defence, is immensely important. It is immensely important because one of the most fundamental objectives of modern international law, and an overriding objective of the UN Charter, is the prevention of war.1 International law on the use of force provides the framework within which the objective recited in the preamble of the UN Charter to ‘save succeeding generations from the scourge of war’ is pursued by the United Nations. Having clear and precise scope and limits of this law is necessary to achieving this lofty objective. Yet the importance of the international law on the use of force is matched by the controversy surrounding the very scope and limits of the law on the use of force.