Sizeable Jewish and Muslim communities lived across large swathes of medieval Western Europe. But all the Muslim communities and almost all the Jewish communities in polities that correspond to present-day England, France, Hungary, Italy, Portugal, and Spain were eradicated between 1064 and 1526. Most studies of ethnoreligious violence in Europe focus on communal, regional, and national political dynamics to explain its outbreak and variation. Recent scholarship shows how the Catholic Church in medieval Europe contributed to the long-term political development and the “rise of the West.” But the Church was also responsible for eradicating non-Christian minorities. Three factors explain ethnoreligious cleansing of non-Christians in medieval Western Europe: (1) the papacy as a supranational religious authority with increasing powers; (2) the dehumanization of non-Christians and their classification as monarchical property; and (3) fierce geopolitical competition among Catholic Western European monarchs that made them particularly vulnerable to papal-clerical demands to eradicate non-Christians. The extant scholarship maintains that ethnoreligious cleansing is a modern phenomenon that is often committed by nationalist actors for secular purposes. In contrast, a novel explanation highlights the central role that the supranational hierocratic actors played in ethnoreligious cleansing. These findings also contribute to understanding recent and current ethnic cleansing in places like Cambodia, Iraq, Myanmar, the Soviet Union, and Syria.