The purpose of this Chapter is to show that today the crime of aggression is an integral part of customary international law. The customary nature of the crime of aggression is derived from the Nuremberg construct of crimes against peace. Both categories of crimes can be perpetrated only by leaders, whether members of the armed forces or civilians. However, on the face of it, there is a dissonance where acts of aggression "short of war" are concerned. The reason is that crimes against peace are expressly restricted to wars of aggression, whereas the crime of aggression is not. This Chapter argues that the discrepancy is more apparent than real, inasmuch as (under the Kampala Amendments of the Rome Statute of the International Criminal Court) the crime of aggression is confined to those acts of aggression that - by their character, gravity and scale - constitute manifest violations of the Charter of the United Nations. There are three cumulative conditions in this formula. To qualify as crimes, acts of aggression must be marked by their intrinsic nature (“character”), seriousness (“gravity”), and magnitude (“scale”). When interlocking, the three conditions create a high threshold that excludes individual culpability for acts of aggression "short of war".