Contemporary International Law ♦ Fall 2025

Prohibiting Threats of Aggression

Edward T. Swaine

Recent events, especially Russia’s invasion of Ukraine, have revived worries about the international regime regulating the use of force. Vastly less attention has been paid to what often precedes such attacks — threats to use force — and the prohibition on them. While the UN Charter and other legal instruments integrate the threats regime with the regime on actual uses of force, the two regimes are increasingly decoupled, in part because only one considers gradations: the use-of-force regime now identifies more serious variants like aggression and crimes of aggression; threats rules, by contrast, do not. This decoupling reflects real differences in the underlying wrongs, but it is also due to bureaucratic history and path dependence, including reluctance to criminalize threats of aggression while the underlying concept of aggression was still being developed.