Abstract. Does war make the state or undermine it? Many argue that pressure from international warfare promoted cooperative statebuilding in Western Europe: monarchs granted parliamentary rights to elites in return for revenues to fight wars. We develop a new theory of cooperative statebuilding that demonstrates how outside threats might instead hinder this process. The key contribution of our model is to highlight how war threats affect—and may weaken—the elite’s demand for constraints on the executive. For landed elites, who depend on the ruler for security against outsiders, war threats undercut their leverage to refuse funding an unconstrained ruler. For merchant elites, war threats may strengthen their leverage too much, causing them to exit the polity rather than fund a hopeless war effort. Only under circumscribed conditions do war threats make a strong parliament more likely to emerge cooperatively, which helps to account for variance in historical European parliaments.