This book provides a systematic analysis of Hobbes, Locke, Rousseau and Kant with respect to international relations. These philosophers belong to the social contract tradition and are considered some of the most influential political theorists. Their ideas have played a role in the formation of national political constitutions and remain very influential both in understanding and legitimising the structure of societies around the world. This book is an innovative analysis of what these thinkers have claimed regarding the relationship between nation states, rather than contributing to the established scholarship on what they have said about individual political societies. Specifically, individual chapters examine war and peace, world governance, inequality, and terrorism.