When insurgent organizations factionalize and fragment, it can profoundly shape a civil war: its intensity, outcome, and duration. In this extended treatment of this complex and important phenomenon, Michael Woldemariam examines why rebel organizations fragment through a unique historical analysis of the Horn of Africa's civil wars. Central to his view is that rebel factionalism is conditioned by battlefield developments. While fragmentation is caused by territorial gains and losses, counter-intuitively territorial stalemate tends to promote rebel cohesion and is a critical basis for cooperation in war. As a rare effort to examine these issues in the context of the Horn of Africa region, based upon extensive fieldwork, this book will interest both scholarly and non-scholarly audiences interested in insurgent groups and conflict dynamics.