Military expenditures are often funded by debt, and sovereign borrowers are more likely to renege on debt-service obligations if they lose a war than if they win one or if peace prevails. This makes expected debt service costlier in peace, which can affect both crisis bargaining and war termination. I analyze a complete-information model where players negotiate in the shadow of power, whose distribution depends on their mobilization levels, which can be funded partially by borrowing. I show that players can incur debts that are unsustainable in peace because the opponent is unwilling to grant the concessions necessary to service them without ﬁghting. This explanation for war is not driven by commitment problems or informational asymmetries but by the debt-induced inefﬁciency of peace relative to war. War results from actions that eliminate the bargaining range rather than from inability to locate mutually acceptable deals in that range.