Nations attempt to reproduce their armed forces for the present and future in the way they were constituted in the past. However, the relationship between military service and citizenship—coupled with processes of globalization, migration, wartime mobilization, and the decline of conscription-based mass armies—has created pressures for the extension of the recruitment base to previously excluded or limited groups. The integration of the U.S. military on the bases of ethnicity, race, sex, gender, and sexual orientation exemplifies how obstacles to integration are raised and overcome, producing military forces that reflect the increasingly diverse populations they serve; thus, allowing excluded groups a greater claim to citizenship rights and allowing nations to draw on the human capital that they hold for purposes of national security. In the past, diversity was believed to mitigate against social cohesion and military effectiveness; however, more recently, emphasis has been on task cohesion and the contribution of diversity to effectiveness.