Security studies, also known as international security studies, is an academic sub-field within the wider discipline of international relations. The field rapidly developed within international relations during the Cold War, examples from the era including the academic works of mid-20th century realist political scientists such as Thomas Schelling and Henry Kissinger, who focused primarily on nuclear deterrence. While the field is mostly contained within political science and public policy programs, it is increasingly common to take an interdisciplinary approach, incorporating knowledge from the fields of history, geography (stressing classical geopolitics), military sciences, and criminology.