This study investigates whether ethnic and other forms of social diversity affect militarization of society. Recent scholarship in economics finds that high diversity leads to lower provision of public goods. At the same time, many conflict studies find that highly diverse societies face a lower risk of civil war, as opposed to relatively more homogenous populations. The authors explore whether diversity prompts governments to militarize heavily in order to prevent armed conflict, which would then crowd out spending on other public goods in a `guns versus butter' trade-off. Thus, `preventive militarization' would explain both outcomes. Yet the authors find the opposite: higher levels of ethnic diversity predict lower levels of militarization. If high diversity lowers the hazard of civil war, as many find, then it does not happen via preventive militarization. If diverse societies spend less on public goods, then this is not because they are crowded out by security spending. The results support those who suggest that diversity may, in fact, pose a lower security threat to states, since it is highly likely that states facing potential social strife would prioritize state militarization.