This study attempts to analyze Japanese foreign policy behavior in the 1905 - 1941 period. The two central themes explored in the analysis are lateral pressure and status inconsistency. To illustrate the themes the study draws upon diplomatic history and social psychology. The study is an exploratory one which offers a theoretical not empirical analysis although some operational measures are offered. A modest attempt is made to demonstrate how diplomatic history and social science, rather than being distinct fields of study, should be fused to achieve a fuller explanatory capability. Moreover the study also attempts, in an equally modest way, to explore the potential relevancy of social-psychology research to the study of international relations, specifically studies on the origins of war. Specifically the study is concerned with why Japan decided to enter the Second World War at the end of 1941. In general it is hoped that the ideas explored will in some way cast some light on the broader question 'why war'.