This second edition of Moral Constraints on War offers a principle-by-principle presentation of the trans-cultural roots of the ethics of war in an age defined by the increasingly international nature of military intervention. Parts one and two trace the evolution of Just War Theory, analyzing the principles of jus ad bellum and jus in bello: the principles that determine under what conditions a war may be started and then conducted. Each chapter provides a historical background of the principle under discussion, an explanation of the principle, and numerous historical examples of its applicat.