The article discusses approaches to the study of the theoretical foundations of the U.S. foreign policy. For decades, the United States has been one of the most important actors in international relations. The post-Cold War period is one of the most important periods in the U.S. foreign policy. At this time, scholars also debate the new role of the United States in the structure of international relations. Singling out the United States as the only center of power, American researchers supported the idea of a “unipolar” world. The ideas of American scholars and researchers dominated the words of American political leaders of the time: the United States is a world leader, and its mission is to establish a new international political and economic order based on liberal democratic values. The ideas of spreading democratic values and the theory of a democratic peace have had a significant impact on the formation and development of the U.S. foreign policy after the Cold War. The article examines the content and essence of these theories, their basic principles, and the reflection of these theories in the foreign policy of the United States.