CYIL Vol. 6, 2015

VERONIKA BÍLKOVÁ CYIL 6 ȍ2015Ȏ international law either. If it were, states would probably not be so reluctant to confer upon the ICC the jurisdiction over this crime and would reach the consensus over the definition already in Rome. At the same time, the debates indicate that the uncertainties relate mainly to the definition of the act of aggression (as the underlying act of state) or, more exactly, of certain forms of this act. 84 Despite that it seems that, again, the core of the definition is not subject to serious contentions. Planning, preparing, initiating or exercising an invasion or attack by the armed forces of a state against the territory of another state without the UN Security Council mandate and outside the self-defence context, would most probably be qualified as a crime of aggression worldwide. There would also likely be consensus that such a crime goes against the very foundations of modern international law and, as such, must not remain unpunished. While political considerations might prevent prosecution, the consensus would remain. It might seem that this brings us back to the history and morality argument. After all, general outrage over an act could stem simply from common abhorrence at barbarity and from the historical experience that such acts could be prosecuted at the individual level. Yet, even if these elements were present, the shared view that a certain act is a crime and those individually responsible for it have to be brought to justice can hardly be qualified otherwise than as an opinio juris, one of the components of a customary rule. 85 The dearth of precedents could suggest that the other component, usus longaevus, is absent. This, however, was not much different with other international crimes in the early 1990s, when the two ad hoc international tribunals were established, and, still, there customary nature was largely accepted. Thus, it seems that in international criminal law, “a clearly demonstrated opinio juris establishes a customary rule without much (or any) affirmative showing that governments are consistently behaving in accordance with the asserted rule”. 86 The predominant support among states for the inclusion of the crime of aggression into the Rome Statute indicates that such a clearly demonstrated opinio juris, as least as far as The previous section argued that the crime of aggression qualifies as an international crime. This section considers whether it is warranted to regard aggression as the supreme international crime. The Nuremberg Tribunal did so, as we saw above, when it held that “to initiate a war of aggression /…/ is not only an international crime; it is the supreme international crime differing only from other war crimes in that it contains 84 See SAYAPIN, S.: The Crime of Aggression in International Criminal Law. Historical Development, Comparative Analysis and Present State, Asser Press, 2014, pp. 75-144. 85 ICJ, North Sea Continental Shelf (Federal Republic of Germany/Netherlands), Judgment, 20 February 1969, par. 74. 86 KIRGIS, F. L.: Custom on a Sliding Scale, American Journal of International Law, 1987, Vol. 81, p. 146. the core of the crime of aggression is concerned, does indeed exist. 4. Aggression as the Supreme International Crime?

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