When debating upon how to react to new styles of warfare in the 21st century, scholars and political leaders often invoke the language of the just war doctrine. However, while terms such as "last resort" and "legitimate authority" are frequently used, their meaning is often vague or improperly used. In what ways can we make the terminology of just war more concrete and meaningful? This study examines the philosophical structure of the just war tradition, in particular focusing on its origins. Through an analysis of the ontological presuppositions of Augustine's arguments on just war, this study explains some of the fundamental assumptions necessary for the just war doctrine to remain coherent. By investigating contemporary attempts to address morality in warfare, this study also explains why major schools of thought (realism, international law, liberalism) fail in this endevour. This book will be of use to scholars of political theory, international relations, and intellectual history. It will also prove useful to researchers who focus political theology, ethics in warfare, and conflict studies.