WHEN DO POWER SHIFTS LEAD TO WAR

We present and test a choice-theoretic model of war decisions during shifts in power. The model assumes a rising state that overtakes a declining state in capabilities. In equilibrium, the declining state yields at a critical point in the transition. War can occur only before that critical time. Power shifts are more likely to lead to war as the challenger becomes more risk-acceptant, the declining state more risk-averse, the expected costs of war decrease, the rising state's dissatisfaction with the status quo increases, and during periods of equality between the two sides. The rate of growth of the rising state's capabilities and the transition point do not affect the probability of war. All these hypotheses are supported by an empirical analysis of all major power dyads since 1815. We also find that expected support from allies must be included in the calculation of a nation's capabilities. The implications of the model for theories of hegemonic decline and war are discussed.