This study models how a nation's military manpower system affects the decision to go to war. Manpower systems differ primarily in how they distribute costs: the volunteer system shares the war's manpower costs broadly, whereas the draft forces a subset of the population to bear a disproportionate share of the load. This difference affects an office-and policy-motivated politician's decision to go to war. The draft induces prowar policy-makers to pursue more wars than the volunteer military does, whereas the volunteer system induces antiwar policy-makers to pursue more wars than the draft does. The manpower systems cannot be generically ranked by efficiency because each makes errors the other avoids, but the volunteer system induces selection of more efficient wars for a large class of plausible preference distributions."Militarized interstate disputes are united historical cases of conflict in which the threat, display or use of military force short of war by one member state is explicitly directed toward the government, official representatives, official forces, property, or territory of another state. Disputes are composed of incidents that range in intensity from threats to use force to actual combat short of war" Jones et al. (1996). 228 WARREN support for war, depending on how citizens are arrayed in the payoff/cost space. In particular, which system leads to more support for war turns on the size of two groups. Group 1 consists of citizens with small benefits of war. The volunteer military has a higher wage bill than does the draft, so citizens with only small benefits from war are unwilling to support a war that would require them to pay for a volunteer military, but they support war under the draft, as long as they do not have to personally fight. If there are a lot of citizens in Group 1, support for war is higher under the draft than under the volunteer military. Group 2 consists of citizens with moderate benefits and large idiosyncratic costs of fighting. They are willing to pay a volunteer to go, but do not support the war if drafted. If there are a lot of citizens in Group 2, support for war is higher under the volunteer military than under the draft. There will usually be people in both groups, so the relative size of these groups determines which system leads to more support.If we further make reasonable assumptions about the distribution of payoffs (singlepeaked), I show that Group 1 citizens are relatively numerous when average benefits are low and Group 2 citizens are relatively numerous when average benefits are high. Overall support for war under either system increases in average benefits. These results together imply that the volunteer military leads to more support than the draft when support under both systems is high and less support than the draft does when support under both systems is low. As a corollary, the volunteer military leads to more war than the draft when antiwar policy-maker controls war policy, as the marginal war with an antiwar policy-maker is one that the citizens strong...