Civil wars are complex, interdependent phenomena that have changed with the introduction of international jihadist groups. Civil war scholarship has not kept pace. This work focuses on rebel alliance formation and durability by introducing a new conception of civil wars based upon the actors and their incentives. Local, sub-state armed groups (LSAGs) join alliances with powerful partners because they need to survive. Conversely, jihadists and state armed sovereigns ally with LSAGs to overcome the information problem. This work advances two original claims: First, LSAGs in civil war do not “ally to win” but rather “ally to survive.” Without alliances, LSAGs would be annihilated. Second, the alliance will either continue with the partners in a state of codependence or end via fragmentation or defection. Alliance durability is regulated by internal LSAG cohesion. This theory is tested on three cases in which Sunni LSAGs in Baghdad allied with al-Qaeda in Iraq (AQI) and the U.S. coalition, 2004-2011. It is further tested on three shadow cases in Mali, Syria, and Yemen.