In his first major work, Scientific Man Vs. Power Politics (1946), Morgenthau was critical of the prevalent contemporary belief that science was the answer to the world’s social and political problems. In his second book, Politics among Nations (1948), he outlined the concept of political realism. Primarily concerned with international relations, this book argued that international politics was shaped by the national interests of sovereign states and was therefore essentially about states ‘keeping power, increasing power and demonstrating power’. As a realist, Morgenthau believed that the policies of nation states should be removed from the universal morals that are experienced by individuals. States should seek to increase their power over any other moral or legal considerations.
Morgenthau’s work was hugely influential, and during the Cold War period he was a policy consultant to the US State Department. However, he was also critical of US foreign policy – opposing the war in Vietnam, for example – and although primarily thought of as a power-politics realist, often overlooked are his endeavours to tease out the connection between moral principles and the politics of necessity, a theme explored in his work In Defense of the National Interest (1951).