Jus ad bellum: history and framework

Empires, kingdoms, and States have relied on military force as a tool of statecraft for millennia - to conquer territory, to protect their territory and citizens, to open and secure trade routes, or to enforce or disrupt alliances, to name just a few. Efforts to regulate, constrain, and even outlaw war and the resort to force have an equally long pedigree, from ancient times to the modern day, and form an essential component of international conflict and security law. This chapter provides a comprehensive overview of the international legal framework regulating the resort to force, the jus ad bellum, from its historical foundations to the prohibition on the use of force in international law and the lawful justifications for the use of force under the United Nations Charter and customary international law.