The ethics of war up to Thomas Aquinas

This chapter explores major developments in concepts of justified warfare and norms of military conduct over nearly 2,000 years. From at least the first millennium BC, ideas about the justice of war and customary norms regulating combat were developed by Western societies. Throughout the ancient and medieval worlds, war was subjected to varying degrees of ethical analysis, as well as being influenced by social pragmatism. Examining a variety of evidence, this chapter argues that the two branches of just war doctrine, jus ad bellum and jus in bello, developed hand-in-hand and should be seen as an integrated whole. This intermingling of jus ad bellum and jus in bello concerns produced a sophisticated and complex body of ethical thought about war—embodied in the systematic analysis of medieval canon lawyers and theologians—and ultimately provided the essential building blocks for modern just war doctrine.