Abyei has proved to be the hardest part of Sudan’s Comprehensive Peace Agreement (CPA) to implement, harder, even, than the determination of the rest of the North-South boundary, or the division of oil revenues. In this personal commentary Douglas Johnson argues that this is the result of a long-term aim of annexation by successive national governments in Khartoum. The recent interventions of US government mediators have made a resolution less, rather than more likely.For sustainable peace there needs to be a recognition of the root causes of the conflict and full implementation of the intent of the Abyei Protocol of the CPA.