One of the most contested questions in the jus ad bellum is whether and when it is lawful for a state to use force unilaterally before it suffers an armed attack. The question took on particular salience in 2002, when the United States claimed – more clearly and assertively than before – that a state could use force to forestall certain hostile acts by its adversaries. Eleven years after that controversial assertion, it is well worth assessing where the debate currently stands and where it is heading.
Because states and scholars use a variety of poorly-defined terms to discuss acts of self-defense in advance of an attack, Part II sorts through the terminology. Part III lays down the basic positions in the historical debate about the legality of such self-defense. Part IV turns to new pressures on self-defense brought on by new actors, new threats, and new technologies. Part V considers the future of pre-emption. It concludes that recent trends in state practice and in scholarship reveal that the timing of a state’s right to use force in self-defense continues to evolve, particularly when the fact patterns implicate terrorist groups or weapons of mass destruction (WMD). Yet certain technological developments make it difficult to predict the degree to which this evolution will continue.
Ashley S. Deeks, Taming the Doctrine of Pre-Emption, in The Oxford Handbook of the Use of Force in International Law, Oxford University Press, 661–678 (2015).