Legality of the use of force in Syria against Islamic State and the Khorasan Group

Abstract

This article critically examines the legality of the use of force in Syria against Islamic State and the Khorasan Group by the US-led coalition and what this reveals about the current scope of the law of self-defence. The author starts by considering Security Council Resolution 2249 and consent as possible justifications for the coalition's use of force. Following this, the justification of self-defence is analysed. The requirement of an occurrence of an armed attack for the claims of collective and individual self-defence is inspected. A further hurdle for the legality of the use of force in Syria is that the international law governing when a state can use self-defence against non-state actors acting outside the state's control is generally unsettled. This article canvases the status quo before scrutinising the justifications invoked by states involved and the international reaction to the use of force in Syria against Islamic State. Subsequent state practice is also examined. Analysis indicates that while there has been general acceptance of the military action in Syria, it is not sufficient to constitute meaningful opinio juris. Thus, this instance is not demonstrative of crystallisation at customary international law and consequently the use of force in Syria is illegal.