Several contemporary theories in the neo-realist corpus, modifies earlier assumptions about unit level behavior. The explanatory value of these theories has to be tested. The aim of this research, was to test the explanatory value of Davide Fiammenghis theory about the security curve, and Nuno P. Monteiros theory about unipolarity. In order to test the theories, a case study was designed where Japans aggression against the USA in 1941, was used as a least-likely case. Inspired by the idea from neo-classical realism, that the perceptions of decisions makers can vary considerably from real conditions, I used primary sources to study the perceptions and calculations inside the Japanese government. Three critical foreign policy decisions, made by the Japanese government in 1940 and 1941 were analyzed. Fimmenghis theory were first rejected, yet when it was modified to fit the condition of asymmetric economic dependence, it fit well the data. The study also indicated, that Monteiros theory can explain state behavior, if a state anticipates that it could end up in unipolar, international system.