This chapter sheds light on external agency at the 'receiving end' of contemporary regionalism, exploring the nature of security regionalism in the Horn of Africa (HoA). It attempts to regionalize security has been institutionalized in the Intergovernmental Authority on Development (IGAD). The chapter reviews that while the IGAD peace processes in Sudan and Somalia were portrayed as inherently regional, closer examination reveals that IGAD as a regional institution. It identifies causal mechanisms between the outcomes of the two processes with the priorities and interests of international actors, considering how international forces have interacted and shaped the relationship between security and regionalism. The chapter draws from long-term field and literature research on Sudan and Somalia which enables the authors to produce a comparative analysis that examines similarities and differences of behaviour among the involved actors. It indicates that the increase in the number of programmes oriented to counter terrorism failed to improve significantly its effectiveness in conflict prevention and resolution.