Treaty law and ICC jurisdiction over the crime of aggression

This article examines the question of who will be subject to International Criminal Court (ICC) jurisdiction with respect to the crime of aggression. One of the most contentious questions in the negotiations regarding the crime of aggression was whether the Court would have jurisdiction over nationals of a state that does not ratify the Kampala Amendments, but which is alleged to have committed an act of aggression on the territory of a state that has accepted the aggression amendments. The question is examined here against the background of the rules in the law of treaties regarding amendments and treaty interpretation. The article considers the legal effect that the resolution adopted by the ICC Assembly of States Parties in New York in December 2017 will have in determining this jurisdictional question. A resolution of an international conference adopted by consensus can, in principle, be regarded as subsequent practice or a subsequent agreement of the parties to the Rome Statute that establishes the authentic interpretation of the Statute within the meaning of the Vienna Convention on the Law of Treaties. It is argued, however, that this particular resolution does not, in itself, provide the definitive answer on the correct interpretation of the Rome Statute. Despite being adopted by consensus, and despite being highly relevant for the interpretation of the Rome Statute and the Kampala Amendments, this resolution does not necessarily amount to a subsequent agreement or subsequent practice that the Court is legally bound to follow. Nevertheless, it is further argued that the position adopted in New York with regard to the jurisdiction of the Court over nationals of states parties that do not ratify the Kampala Amendments is the correct legal position and the one that the Court ought to adopt. The answer to the question over whom the Court will have jurisdiction with respect to aggression is to be found in Rome rather than in Kampala, or even in New York. We argue that the key to addressing this issue is to understand how the amendment provisions of the Rome Statute work in conjunction with basic principles of the law of treaties