This dissertation examines the emergence, survival, performance, and national impact of rebel parties following negotiated settlements. Building on a growing literature examining the environmental and organizational factors affecting insurgent-to-party transformations, this dissertation asks why some insurgent organizations thrive as political parties in post-conflict environments and others fail to make such a transformation. I propose that foreign actors play a pivotal role in the formation of what I call “protégé parties,” which are better equipped to make the transformation into political parties than other rebel groups. Further, different kinds of sponsors have varying effects on transformation. Empirical analysis supports these propositions, finding that protégé parties with authoritarian sponsorship are better equipped to develop than those backed by democracies or no one.