"war of aggression [...] contains within itself the accumulated evil of the whole"

Abstract

The prohibition of aggression – which may be regarded as the “imperative core” of the prohibition of the use of force – is one of the most debated rules of international law. The concept of aggression was long marked by doctrinal uncertainty, and until 1974 no consensus had been reached on a workable definition of the concept. Although the annex to United Nations General Assembly Resolution 3314 (XXIX) eventually defined the act of aggression, the question of individual criminal responsibility remained unresolved for decades following the adoption of the Rome Statute. Thus, until the Kampala Amendment, the prohibition of aggression remained merely nominal within the Statute. This study examines the normative development of the prohibition of aggression from the Nuremberg Judgment to the present day, with particular regard to the doctrinal distinction between state and individual responsibility, as well as to the sui generis jurisdictional regime of the International Criminal Court. The analysis argues that, despite ongoing conceptual debates, the prohibition of aggression has become a stable peremptory norm, and that the substantive definition of the crime of aggression has been formulated with the degree of precision required of an international crime. Nevertheless, the stricter jurisdictional regime governing the crime of aggression significantly complicates the ICC’s ability to exercise jurisdiction, and its harmonisation – which has become more urgent than ever in light of Russia’s aggression against Ukraine – has still not been achieved as of 2025.