Examining the relationship between regime type and defense effort provides evidence for reformulating theories of democratic peace. Consistent with liberal theories, regime type has substantively and statistically significant effects. In times of peace, democracies bear lower defense burdens than other states and keep proportionately fewer soldiers under arms. During times of war, however, democracies try harder and exert greater defense effort than non-democracies. Contrary to the results of some recent studies, all other things being equal, the arsenal of democracy appears to out-gun its opponents when it counts. Examining three components of democracy separately indicates that a largely overlooked factor, political competition, tends to drive these outcomes. Executive constraints are also associated with increased defense effort during war. But there is little evidence that wide participation or large winning coalitions have the predicted effects on defense effort. The results point to the flexible quality of defense effort in democracies, which is theoretically and empirically accounted for by the competitive political environment rather than institutional factors favored by existing theories.