Among war scholars, power shifts between states have been a persuasive explanation of the occurrence of war, with Power Transition Theory (PTT)r in particular, demonstrating powerful and systemic research. Their deduction of the conditions of war matches the empirical phenomena. However, extant studies fail to explain why in some cases power shifts and dissatisfaction lead to war while in some cases they do not. This paper argues that the story of power shifts and war is not completely told. There are other options that states can choose from in a period of power parity. For instance, the rational choice approach can discover and compare the utilities of the options. To be specific, scholars who are concerned for power shifts have taken states as individual actors in the international system for granted, but the goal, preference orders, and utilities of actors should he illuminated. Hence, this paper adopts an interaction framework of actors to demonstrate how states may act and react in a period of power shifts. Two cases, namely, Britain and Germany before WWII and the U.S. and Japan in 1980s, demonstrate how well the interaction framework fits the reality. Overall, the framework discloses the interaction of the players and strengthens the explanation of PTT. More importantly, the story behind power shifts and war is fully told.