Self-Defence Against Non-State Actors After 9/11

The right of states to use force in self-defence occupies a central yet deeply contested place in contemporary international law. Enshrined in Article 51 of the UN Charter as an exception to the general prohibition on the use of force in Article 2(4), self-defence has traditionally been understood as a narrowly circumscribed right exercised in response to an armed attack attributable to another state. However, the rise of transnational armed groups and the security shocks of the post-9/11 era have placed unprecedented strain on this framework. This blog examines the scope of self-defence against non-state actors and situates the debate within broader theoretical disagreements between realism and institutionalism in international security studies.