Hans Joachim Morgenthau (February 17, 1904 – July 19, 1980) was one of the major twentieth-century figures in the study of international politics. Morgenthau's works belong to the tradition of Realism in international-relations theory, and he is usually considered, along with George F. Kennan and Reinhold Niebuhr, one of the three leading American realists of the post-World War II period. Morgenthau made landmark contributions to international relations theory and the study of international law. His Politics Among Nations, first published in 1948, went through five editions during his lifetime.