Despite the common belief that alliances are reliable, states abrogate their alliance commitments frequently. Previous studies reveal that various factors motivate states to take opportunistic...Show moreDespite the common belief that alliances are reliable, states abrogate their alliance commitments frequently. Previous studies reveal that various factors motivate states to take opportunistic behaviors, and the change in an alliance member’s military power is the most influential cause. Nevertheless, existing literature provides insufficient delineation on how the power change leads states to violate their alliance commitments. In this paper, I unravel the causal process of the abrogation of alliance commitment by analyzing the German-Soviet Non-Aggression Pact and the French-Czechoslovak Alliance using process-tracing. I provide evidence that the change of power reshapes states' preferences by creating a time-inconsistency problem, leading them to pursue the new preference of violating the alliance commitment. Although other minor elements contribute to states’ cost-benefit calculations, results show that the change in military capability affects the cost of honoring the commitment. When an alliance member’s power increases, the cost of self-defense reduces, while a decrease in power raises the cost of assisting an ally. An analysis of the aforementioned cases supports the time-inconsistency problem model in alliance politics. The time-inconsistency problem model contributes to sharpening the existing knowledge of alliance politics.Show less
