Article 2 (4) of the United Nations Charter prohibits the threat or use of force in international relations, a prohibition that is accepted as customary international law. 1 However, at the San Francisco Conference (1945) middle-level states were unwilling to give up their 'inherent' right to use force in self-defence. Article 51 of the Charter therefore allows a shortterm limitation 2 to article 2 (4) whereby a state may have recourse to individual or collective self-defence 'if an armed attack occurs. .. until the Security Council has taken measures necessary to maintain international peace and security'. The affirmation of a right to self-defence undermines the absolute nature of the prohibition against unauthorised use of force in article 2 (4). Unsurprisingly, therefore, states have sought to bring almost any unilateral use of force within the legal ambit of selfdefence, so much so that as early as 1970 Professor Franck famously asked: 'Who killed article 2 (4)?' 3 In the twenty-first century, article 2(4) is widely understood as being in a state of 'grave weakness', even 'on the brink of clinical death or in intensive care'. 4 1 In the Nicaragua case neither party challenged the customary international law status of UN Charter, article 2(4); Military and Paramilitary Activities in and against Nicaragua (Nicaragua v. United States of America), (Merits) 1986 ICJ Reports 14, judgment of 27 June 1986, para. 188 ('Nicaragua'). For an overview of contemporary international law relating to the use of force see Crawford, James 2012. Brownlie's Principles of Public International Law, Oxford University Press, 8th ed., chapter 33. 2 Jean D'Aspremont notes that UN Charter, article 51 does not derogate from article 2(4) but imposes a temporary limitation upon it; D'Aspremont, Jean 2014. Mapping the Concepts behind the Contemporary Liberalization of the Use of Force in International Law,