During the 1920s new centres, institutes, schools, and university departments devoted to teaching and research in international relations were created in Europe and North America. In addition, private organizations promoting the study of international relations were formed, and substantial philanthropic grants were made to support scholarly journals, to sponsor training institutes, conferences, and seminars, and to stimulate university research.

Three subject areas initially commanded the most attention, each having its roots in World War I. During the revolutionary upheavals at the end of the war, major portions of the government archives of imperial Russia and imperial Germany were opened, making possible some impressive scholarly work in diplomatic history that pieced together the unknown history of prewar alliances, secret diplomacy, and military planning. These materials were integrated to provide detailed explanations of the origins of World War I. Among such works several are particularly noteworthy, including Sidney Bradshaw Fay’s meticulous The Origins of the World War (1928), which explored prewar diplomacy and alliance systems; Bernadotte E. Schmitt’s The Coming of the War, 1914 (1930) and Triple Alliance and Triple Entente (1934); Pierre Renouvin’s The Immediate Origins of the War (1928); Winston Churchill’s The World Crisis (1923–29); and Arnold J. Toynbee’s The World After the Peace Conference (1925). There also were extensive memoirs and volumes of published documents that provided much material for diplomatic historians and other international relations scholars.

The newly created League of Nations, which ushered in the hope and expectation that a new and peaceful world order was at hand, was a second subject that captured significant attention. Some of the international relations schools that were founded in the interwar period were explicitly created to prepare civil servants for what was expected to be the dawning age of international government. Accordingly, intensive study was devoted to the genesis and organization of the league, the history of earlier plans for international federations, and the analysis of the problems and procedures of international organization and international law.

The third focal point of international relations scholarship during the early part of the interwar period was an offshoot of the peace movement and was concerned primarily with understanding the causes and costs of war, as well as its political, sociological, economic, and psychological dimensions. Interest in the question “Why war?” also brought a host of social scientists, including economists, sociologists, psychologists, and even mathematicians—all of whom were pioneers in the intellectual movement known as behaviourism—into active participation in international studies for the first time.

In the 1930s the breakdown of the League of Nations, the rise of aggressive dictatorships in Italy, Germany, and Japan, and the onset of World War II produced a strong reaction against international government and against peace-inspired topics in the study of international relations. The moral idealism inherent in these topics was criticized as unrealistic and impractical, and the academic study of international relations came to be regarded as the handiwork of starry-eyed peace visionaries who ignored the hard facts of international politics. In particular, scholars of international relations were criticized for suggesting standards of international conduct that bore little resemblance to the real behaviour of nations up to that time. As the desired world of peaceful conflict resolution and adherence to international law grew more distant from the existing world of aggressive dictatorships, a new approach to the study of international relations, known as realism, increasingly dominated the field. Nevertheless, the scholarly work on world affairs of the early interwar period, despite the decline in its reputation and influence, was extensive and sound, encompassing the collection and organization of large amounts of important data and the development of some fundamental concepts.

Some topics of study in international relations that are still considered novel or of recent origin were already being vigorously explored in the interwar period. Indeed, a brief review of these topics tends to undermine the image of the interwar period as one dominated by moralistic ideas. The topics include the causes of wars; the relationship between international affairs and the problems of racial and ethnic minorities; the effects of population change on foreign policies; the effects of nationalism, imperialism, and colonialism; the strategic aspects of international relations, including the importance of geographic location and spatial relationships (geopolitics) for military power and the influence on governments of what later was called the “military-industrial complex”; the implications of economic inequalities between countries; and the role of public opinion, national differences, and cultural orientation in world affairs. Although these earlier studies tended to be somewhat short on theory and long on description, most of the topics examined remain relevant in the 21st century.

The scholarly contributions of some individuals in the 1930s were particularly noteworthy because they foreshadowed the development of international relations studies after World War II. Harold D. Lasswell, for example, explored the relationships between world politics and the psychological realm of symbols, perceptions, and images; Abram Kardiner and his associates laid the groundwork for an approach, based on a branch of anthropology known as culture-and-personality studies, that later became a popular but short-lived theory of international relations; Frederick L. Schuman, setting a style that is still followed by interpreters of foreign policy and by journalists, synthesized analytic commentary with accounts of current international events; Quincy Wright investigated numerous aspects of international behaviour and war as head of one of the first team research projects in international relations; and E.H. Carr, Brooks Emeny, Carl J. Friedrich, Schuman, Harold Sprout, Nicholas Spykman, and others developed the main lines of what became the “power-politics” explanation of international relations, also known as realism. In 1937 the Spanish poet, historian, philosopher, and diplomat Salvador de Madariaga, founder of the College of Europe, relied upon his experience in working with the League of Nations Secretariat in Geneva to describe the gap between what was being said or written about international relations and what was actually happening.

The broadened definition and scope of the study of international relations were among the fundamental contributions of scholars of the interwar period. Many of these innovators were enlisted by governments during World War II for work in intelligence and propaganda, as well as other aspects of wartime planning. In this respect the war stimulated systematic social-scientific investigations of international phenomena. It also led to important technological advances—notably the computer—that would later have a major impact on the study of international relations.

In other ways World War II was a divide for academic international relations. The war itself brought about a drastic change in the agenda of world politics, and the postwar intellectual climate was characterized by a marked shift away from many earlier interests, emphases, and problems. In the early postwar years there was a quest for analyses that would cut through the details of studies of myriad international topics to produce a general understanding of common elements and a clear view of the fundamental nature of international politics. There was also a growing interest in developing theories that could help to explain the major issues of the changing international scene. New security issues emerged, including the issue of nuclear weapons, which led to extensive writings on deterrence as a basis of strategic stability. Bernard Brodie’s treatise on nuclear deterrence was highly influential, as was the work of Herman Kahn, Glenn Snyder, Thomas C. Schelling, Henry A. Kissinger, and Albert Wohlstetter. Other issues that were addressed in the vast literature of international relations include international, and especially European, integration; alliances and alignment, such as the North Atlantic Treaty Organization (NATO); ideologies; foreign-policy decision making; theories about conflict and war; the study of low-intensity conflict; crisis management; international organizations; and the foreign policies of the increasing number of states that became part of the international system in the mid- to late 20th century.