Since their first publication, the four volumes of the Cambridge History of American Foreign Relations have served as the definitive source for the topic, from the colonial period to the Cold War. The fourth volume explores the conditions in the international system at the end of World War II, the American determination to provide leadership, and the security dilemma each superpower posed for the other. This revised and expanded edition incorporates recent scholarship and revelations, carrying the narrative through the years following the end of the Cold War into the administration of Barack Obama. The character of the American political system is explored, including the separation of political powers and the role of interest groups that prompted American leaders to exaggerate dangers abroad to enhance their domestic power. This new edition examines the conditions in the international system from the end of World War II to the present, focusing on the American determination to provide world leadership.