CYIL vol. 12 (2021)

CYIL 12 (2021) PREEMPTIVE SELF-DEFENCE IN CYBERSPACE supervenes’ customary international law. It rather demonstrates that in the field in question […] customary international law continues to exist alongside treaty law. The areas governed by the two sources of law thus do not overlap exactly, and the rules do not have the same content.” 40 As concerns the justification of a preemptive self-defence in the cyberspace, this mode of argumentation would thus not be substantiated as the occurrence of an armed attack constitutes the core condition. This viewpoint corresponds to the prevailing opinion of States in international practice. 41 2. Rejection of the Caroline Case concept The attempts to claim a broader scope of the customary right of self-defence going beyond Art. 51 in order to encompass a preemptive action are based on the Caroline Case. This 19 th century dispute between the United States and Britain over the legality of the British raid on the steamer Caroline , held in the hands of insurgents against the British rule in Canada and anchored in the US port, was marked by the well-known Webster formula acknowledging the right to preemptive self-defence. In the framework of the diplomatic exchanges between the two governments, the United States Secretary of State Daniel Webster noted in a letter of 24 April 1841 that, for the British action to be lawful, it has to prove the “necessity of self-defence, instant, overwhelming, leaving no choice of means, and no moment for deliberation”, and that “the act, justified by the necessity of self-defence, must be limited by that necessity, and kept clearly within it”. 42 According to historical analysis, the US and UK positions diverged as regards the facts of the dispute. It is interesting that although the Webster formula expresses an opinion of a party to a dispute, it has been referenced, by the proponents of preemptive self-defence, as an authoritative pronouncement on international law and a valid confirmation. For example, Christopher Greenwood notes in 2002: “[T]he right of anticipatory self- defence is quite narrowly defined. Ever since the United Kingdom-US exchange in what has become known as the Caroline case in 1837–38, the right has been confined to instances where the threat of armed attack was imminent. In my opinion, that still reflects international law and, in so far as talk of a doctrine of ‘pre-emption’ is intended to refer to a broader right to respond to threats which might materialise some time in the future, I believe that such a doctrine has no basis in law.” 43 Similarly, Michael Wood, affirms that “[a]n imminent attack suffices, see, for example, the exchange of letters following the Caroline incident” 44 . In a statement to the House of Lords on 21 April 2004, the Attorney-General Lord Goldsmith presented the Government’s view on “the legitimacy of pre-emptive armed 40 Nicaragua Case, op. cit. note 21, p. 716. 41 See the detailed analysis of State practice, notably of Israeli attacks of 2 December 1975 on the Palestinian camps in Lebanon and in 1981 on the nuclear reactor Osirak in Iraq and regarding the US-led intervention in Iraq in 2003, for example in Cassese, A., op. cit. note 38, pp. 1336–1341. 42 Correspondence between Great Britain and the United States, respecting the Arrest and Imprisonment of Mr. McLeod, for the Destruction of the Steamboat Caroline (March, April 1841), 29 British and foreign state papers (1840–41) , p. 1138. 43 Memorandum of Professor Christopher Greenwood (October 2002) cited in Wilmshurst, E., Principles of international law on the use of force by states in self-defence , ILPWP 05/01, 1 October 2005, para. 24, p. 37, available at . 44 Cited in Principles of international law on the use of force by states in self-defence , ibid . p. 39.

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