Abstract How is order achieved in a realm in which every elite commands both economic and military resources, and no stable institutions of power exist? We depict coalition formation in the feudal world as a series of non-binding agreements between elites who can move in and out of the coalition, through peaceful and violent means. We derive conditions under which the realm unites under one rule — a grand coalition, or remains fragmented. We motivate our analysis with key historical episodes in medieval Europe, from the Frankish Kingdom in the 5th to 10th centuries and England in the 11th to 15th centuries.