Hans Morgenthau is a legendary American diplomat, international law theorist, geopolitician and mentor of Henry Kissinger, who theoretically prepared the ground for the development of all the basic concepts of US foreign policy. His analysis and foreign policy understanding of the extensive system of relationships between countries, structures, organizations and non-state entities became the dominant texts in the field of world politics in the second half of the 20th century. It is with his works that a structural revision of the discursive foundations of international law and its application in various fields begins, which has led international politics to the current situation, and the issues of war and peace that he raised finally form the understanding among war researchers of when a war should be considered legitimate and when not . Back in the 1960s, he developed an original concept of international relations, which was the basis of American foreign policy, later called political realism. In fact, it is from this book that modern international law begins, with its extensive system of justice, checks and balances, international conventions and the special role of the UN and the Security Council. Without this book, the modern system of international relations cannot be understood.