Do states experience more peace under female leadership? We examine this question in the context of Europe over the 15th-20th centuries. We instrument queenly rule using gender of the first born and whether the previous monarchs had a sister. We find that polities led by queens participated in war more than polities led by kings. Moreover, aggressive participation varied by marital status. Single queens were attacked more than single kings. However, married queens attacked more than married kings. These results suggest that asymmetries in the division of labor positioned married queens to be able to pursue more aggressive war policies.