CYIL Vol. 6, 2015

AGGRESSION ȃ THE SUPREME INTERNATIONAL CRIME OR NOT A CRIME AT ALL? A detailed analysis of the definitional debate is provided elsewhere. 80 Here, it suffices to recall that two issues primarily at stake are the clarity of the definition and its customary nature. Some consider that “ the definition, suffering from overbreadth and vagueness, does not provide sufficient notice to potential defendants”. 81 The vagueness is to be caused by the imprecise language of both the Kampala amendment and the UN Charter to which the amendment refers. It is true that the two texts might, and most probably will, create certain problems of interpretation. Yet, this is not specific for the crime of aggression and it falls under the competence of the ICC – or of national courts applying national Criminal Codes – to resolve such problems. As long as the definition is reasonably clear and concrete for individuals to understand that certain acts are prohibited, the rule containing it can serve as a legal basis for the prosecution of international crimes. It would be hard to deny that at least the core of the definition meets this criterion. The customary nature of the definition has also been contested. Drawing attention to the dearth of relevant precedents, Glannon, for instance, claims that “in light of state practice, the /…/ assertion that the crime of aggression is part of contemporary customary international law is untenable”. 82 Two remarks are warranted in this context. First, it is not certain that an international crime has to have a legal basis in international custom , as opposed to international conventions. In the Tadić Case the ICTY accepted that the rule whose infringement would give rise to international crimes (war crimes in the case at hand) could be customary or belong to treaty law. 83 Although theTadić dictum was closely linked to the interpretation of Article 3 of the ICTY Statute, it could have broader implications. Yet, if used to consider whether a certain act qualifies as an international crime, it would most probably only apply to general, widely accepted treaty instruments which have been in force for some time and have not been significantly opposed (such as the 1948 Genocide Convention or the 1949 Geneva Conventions). The Rome Statute could be such a treaty. Since, however, a defined crime of aggression has been included to it rather recently and since this inclusion has not been uncontested, the Statute of itself could hardly constitute the sufficient legal ground for the qualification of the crime of aggression. The debates surrounding the adoption of the Kampala definition would, moreover, suggest that there is no ready-made definition of the crime of aggression under customary position after the adoption of resolution RC/Res.6, on the crime of aggression, in Review Conference of the Rome Statute of the International Criminal Court, Official Records, 2010, pp. 122-127. 80 See, for instance, SCHEFFER, D.: The Complex Crime of Aggression under the Rome Statute, Leiden Journal of International Law , 2010, Vol. 23, pp. 897-904; STAHN, C.: The ‘End’, the ‘Beginning of the End’ or the ‘End of the Beginning’? Introducing Debates and Voices on the Definition of ‘Aggression’, Leiden Journal of International Law , 2010, Vol. 23, pp. 875-882.

81 GLENNON, M. J.: The Blank-Prose Crime of Aggression, op. cit., p. 88. 82 GLENNON, M. J.: The Blank-Prose Crime of Aggression, op. cit., p. 74. 83 ICTY, Prosecutor v. Duško Tadić, Case No. IT-94-1-AR72, op. cit., par. 94.

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