Between the 1870s and 1930s, American social reformers, working closely with the US government, transformed sexual vice into an international political and humanitarian concern. As these activists worked to eradicate prostitution and trafficking, they promoted sexual self-control for both men and women as a cornerstone of civilization and a basis of American exceptionalism. Empire of Purity traces the history of these efforts, showing how the policing and penalization of sexuality was used to justify American interventions around the world.