In the last two decades or so, legal pluralism in family law has been at the center of scholarly attention. The literature is compartmentalized into two regional foci between postcolonial and post-imperial societies, on the one hand, and Western liberal democracies, on the other. Such regional clustering is often undergirded by a normative bias around the incompatibility of plural family law systems governing members of different religious communities with the legally unified and secular character of modern nation-states. This paper is an invitation to reconsider the relationship between plural family law systems and the modern nation-state in terms of a certain form of population politics that is driven by the idea of cultural homogeneity. Drawing on the minutes of the Lausanne Peace Conference in 1922/23 and secondary sources, the paper suggests that legal pluralism in family law is not an historical anomaly or deviation, but instead an unintentional outcome of the international diplomacy that shaped population politics in the first half of the twentieth century. Plural family law systems have completed their transformation in the aftermath of the World War II into institutional mechanisms for religious “unmixing” within the borders of a sovereign nation-state.