Sociology as a teaching discipline and a public discourse was constructed during the final two decades of the nineteenth century and the first decade of the twentieth in the great cities and university towns of France, the United States, Britain, Germany and, a little later, Russia. The enormous spectrum of human history that the sociologists took as their domain was organised by a central idea: difference between the civilisation of the metropole and other cultures whose main feature was their primitiveness. A social science based on the social relations of empire must deal with race, and a social science concerned with evolutionary progress and hierarchies of populations must deal with gender and sexuality. Sociologists were expected, as scientists, to provide moral and political teaching. Their teaching especially addressed the dilemma that was inescapable for men of the liberal bourgeoisie: the tension between material privilege and reforming principle.