The Fight Against the “Islamic State” in Syria: Towards the modification of the right to self-defence?

This article analyses whether the military operation against the “Islamic State” in Syria led to a modification of the right to self-defence in customary international law. It outlines the arguments presented by some States in favour of a right to self-defence against the IS as a non-State actor. It also explains that, in contradiction with the traditional temporal understanding of the right to self-defence, some of the States intervening in Syria assert a right to react to imminent armed attacks or even to a simple threat of armed attacks committed by the IS. This article shows that there is limited international acceptance of a broad right to self-defence as a justification for the military involvement in Syria. It concludes that neither a right to self-defence against a non-State actor, nor a right to self-defence in reaction to potential future attacks, has crystallised in customary international law. However it acknowledges that the fight directed against the IS in Syria constitutes another step towards the emergence of a customary right to self-defence against non-State actors in response to current or future armed attacks.