Torbjorn L. Knutsen introduces ideas on international relations expressed by thinkers from the High Middle Ages to the present day, and traces the developments of four ever-present themes: war, wealth, peace and power. The book counters the assumption that international relations has no theoretical tradition and shows that scholars, soldiers and statesmen have been speculating about the subject for the last 700 years. Beginning with the roots of the state and the concept of sovereignty in the Middle Ages, the author draws upon the insights of outstanding political thinkers. Clearly and succinctly the theories of Aquinas, Machiavelli, Hegel, Rousseau, Bentham, Marx and Lenin amongst others are discussed and analysed. The ideas of these thinkers are placed in context with the societies and intellectual ideas that produced them. The text is fully revised and updated to include the place of international relations after the Cold War and new ways of thinking opened up by developments in information technology.