Weak sovereignty and interstate war

International agreements save the costs of war, but complying with their terms can be costly. We analyse a model of interstate crisis bargaining in which one state may be unwilling or unable to make a costly investment that guarantees its subjects' compliance. In equilibrium, peace is assured when the domestic government is militarily strong enough to demand terms that its subjects tolerate. When the domestic government is militarily weaker, peace requires that the foreign state compensate it for either the costs of enforcement or its subjects' violations, and these prospective costs of peace may also lead the foreign state to solve the enforcement problem with war because peace is relatively costly. We also show that war due to enforcement problems is more common in militarily weak states and that equilibria at which the foreign state subsidizes enforcement are more common when the costs of violation fall disproportionately on the domestic state. The American invasion of Mexico in 1916 and the Red Army's peaceful withdrawal from East Germany in 1989 demonstrate the model's usefulness.