While the theoretical literature maintains that strategic coordination is one of the keys to successful rebellion, anti-governmental campaigns are not necessarily synchronized across rebel groups in observed civil wars. To resolve this discrepancy, we develop a dynamic and spatial model of rebellion that illustrates patterns of contagious challenges against a government. As battles evolve, more rebels are inclined to "bandwagon," joining the ongoing war because the government is gradually revealed to be weak and because accumulated challenges shift the balance of power away from the government. Our theory also addresses why rebel movements often spread across the periphery and can eventually reach the heartland as if a siege shrinks. We delineate four geographic patterns of rebellion and then classify into them the Yugoslav Wars and other historical incidents.