Alas, the controversy continues. Indeed, although Article 51 UN Charter permits the exercise of self-defence ‘if an armed attack occurs’, a number of authors were quick to point out that the provision did not abrogate the pre-existing customary right of anticipatory self-defence. In addition, they stressed that, in a world gone nuclear, it would be absurd to expect States to await the first – and potentially devastating – blow. In accordance with the famous Webster formula, legacy of the 1837 Caroline incident, States should be allowed to resort to armed force when faced with an imminent threat of attack giving rise to a ‘necessity of self-defence, instant, overwhelming, leaving no choice of means, and no moment for deliberation’. For most of the Charter era, however, a majority of legal doctrine has cautioned against such broad reading of self-defence, allegedly incompatible with the text and aim of Article 51. More importantly, absent an unequivocal precedent receiving broad international support, it arguably did not experience a breakthrough of any sort. Rather, it kept a slumbering existence, fuelling a never-ending doctrinal debate, and dangling over the Ius ad Bellum like the Sword of Damocles.

After the 9/11 terrorist attacks the Sword of Damocles came down hard and unexpectedly. The unprecedented attacks against United States territory led US officials and policy-makers to engage in a fundamental reappraisal of the global security environment, culminating in the adoption by the Bush administration of the US National Security Strategy (NSS) in September 2002.