It is difficult to read both the theoretical literature in political science on the causes of war and historians' case studies of the origins of particular wars without being struck by the difference in their respective evaluations of the importance of domestic political factors. Whereas historians devote considerable attention to these variables, most political scientists minimize their importance. Domestic political variables are not included in any of the leading theories of the causes of war; instead, they appear only in a number of isolated hypotheses and in some empirical studies that are generally atheoretical and noncumulative. This gap is troubling and suggests that political scientists and historians who study war have learned little from each other. A greater recognition of the role of domestic factors by political scientists would increase the explanatory power of their theories and provide more useful conceptual frameworks for the historical analysis of individual wars.

This study takes a first step toward bridging this gap by examining some of the disparate theoretical literature on domestic politics and war. It examines the relationship between national attributes and war behavior, the relative likelihood of democratic and non-democratic regimes going to war, Marxist and liberal theories regarding the impact of economic structure, the influence of nationalism and public opinion, and the scapegoat hypothesis. First, however, this article takes a closer look at the different treatment of domestic sources of war by political scientists and historians.

Are there really lessons of the past? The past is certainly a source of knowledge, our only source of knowledge given the flow of time, but, strictly speaking, it does not teach lessons. By lessons I mean maxims for attaining particular outcomes in the present or future: for example, Si vis pacem, para helium, or it is better for a prince to be feared than loved. Insofar as these maxims seem to offer guidance for policymakers, they are usually psychological, not historical. They supposedly summarize human traits that persist regardless of changing historical contexts. Other examples might include the notion that appeasement encourages aggression or that “military decision makers will tend to overestimate the feasibility of an operational plan if a realistic assessment would require forsaking fundamental beliefs or values.” Identification of such allegedly constant traits was the goal of philosophical history and may have seemed an appropriate program for historians during the Enlightenment and their policy-studies heirs. Subsequent historians, however, have usually sought to describe changing societal contexts or outcomes.

Explanations of the origins of World War II tend to emphasize either deliberate, if failed, choices or inexorable processes. The first view indicts Adolf Hitler's aggrandizing choices and preference for violence, and questions the judgment and strategy of the appeasers, personified, correctly or not, by Prime Minister Neville Chamberlain. The second view broadens the focus, pointing to secular changes in relative power between states; to the relation between states' commitments and their ability to uphold and protect them; and to domestic, economic, and cultural dynamics that individually, or in combination, predisposed the situation to conflict. Attention to both dimensions is necessary to appreciate Britain's strategy as the central axis of diplomacy and rivalry with Germany in the 1930s and to distill the “lessons” of the origins of the war.

In the 1930s, Britain took over the mantle of maintaining the status quo vis-à-vis Germany. Chamberlain and his associates faced the classic issue of judging the nature of its adversary's ambitions. Morgenthau captured the dilemma for Britain in this period: “While it would be fatal to counter imperialistic designs with measures appropriate to a policy of the status quo, it would be only a little less risky to deal with a policy [of an adversary] seeking adjustments within the status quo as though it were imperialistic.”