War has its own momentum: How windows of opportunity prevent negotiated settlements

Why do wars continue even when their original causes are resolved? I offer a rationalist explanation: wars end in a negotiated settlement only when wartime and peacetime balances of power are approximately equal. Since fighting tends to shift the wartime balance of power, war creates its own commitment problems which can preclude a peaceful settlement—even after its initial causes have become irrelevant. In contrast to previous work, I show how these commitment problems arise without any exogenous cause. Aside from the motivating puzzle, this finding accounts for two empirical trends: why costlier wars are shorter and more likely to end peacefully; and why wars are not more likely to end the longer they last, even though more information has been revealed. I then illustrate the model using the Iran-Iraq War. I also derive practical implications for military intervention and military strategy. The article concludes by proving that, for purely rational reasons, a peaceful settlement tends to become less likely the longer a war lasts.