Economic studies of military manpower systems emphasize the advantages of voluntarism under all but the most total threats, but this explains neither the persistence of institutionalized conscription in many states nor the timing of shifts from such conscription systems to volunteer militaries. Traditional explanations focus on external threat levels, but this has also proven unsatisfying. We theorize that threat variables establish the state’s baseline need for manpower, but structural economic variables determine whether the necessary manpower can be more efficiently obtained by conscription or voluntarism. Using a new data set of 99 countries over 40 years, we find that states with British origins are less likely and those experiencing greater external threat are more likely to employ conscripts. Most importantly, states with more highly regulated labor markets are more likely to employ conscripts, which suggests that, controlling for a number of relevant factors, labor markets matter in military manpower decisions.