We provide a new perspective on how domestic factors shape the prospects for international cooperation. Internal arms, specifically conscription, signal a willingness and suitability to be a dependable ally. Possessing ineffective military forces inhibits a state’s ability to assist prospective allies and renders a state less able to deter threats on its own. This exemplifies an instance where the trade-off between arms and allies does not apply. Using new data on the military recruitment policies of states since 1816, we find that adopting a conscription-based recruitment system in the previous five years makes a state more likely to form an alliance in the current year, even when accounting for a heightened threat environment.