According to a leading rationalist explanation, war can break out when a large, rapid shift of power causes a credible commitment problem. This mechanism does not specify how inefficient fighting can resolve this cause, so it is an incomplete explanation of war. We present a complete information model of war as a sequence of battles and show that although opportunities for a negotiated settlement arise throughout, the very desirability of peace creates a commitment problem that undermines its likelihood. Because players have incentives to settle as soon as possible, they cannot credibly threaten to fight long enough if an opponent launches a surprise attack. This decreases the expected duration and costs of war and causes mutual deterrence to fail. Fighting's destructiveness improves the credibility of these threats by decreasing the benefits from continuing the war and can eventually lead to peace. In equilibrium players can only terminate war at specific windows of opportunity and fighting results in escalating costs that can leave both players worse off at the time peace is negotiated than a full concession would have before the war began.