This paper examines inter-ethnic conflict over grazing land previously accessed as common property. It presents results of a study undertaken in Mieso district of eastern Ethiopia where two ethnic groups maintain different production systems – pastoral and agropastoral. The historical change in land use by one of the ethnic groups, resource scarcity, violation of customary norms, power asymmetry and livestock raids are among the factors that have contributed to the recurrence of conflict. Particularly important is the role of raids in triggering conflict and restricting access to grazing areas. Socio-economic and political factors are responsible for power asymmetry and the increasing scale of raids. An increase in the frequency of violence and a decline in the capacity of customary authority in conflict management advance the role of the state in establishing enforceable property rights institutions. This will succeed only if policies and interventions are redirected at suppressing incentives for violence, establishing new institutional structures in consultation with clan elders of both parties, and building internal capacity to monitor conflict-triggering events.