Why do strong opposition party organizations emerge in some democratizing countries, while those in others remain weak or quickly fragment on ethnic lines? This book offers an explanation for why opposition parties vary in organizational form, cohesion, and mobilizational reach. The book draws upon an in-depth analysis of three countries in Anglophone Africa: Zimbabwe, Zambia, and Kenya. Though these countries share similar institutional frameworks, including electoral rules, party development has taken a different route in each. The explanation emphasizes the ways in which historical legacies interact with strategic choices to produce different trajectories of party development. In terms of the role of history, the book argues that strong opposition parties are more likely where authoritarian states relied on alliances with corporate actors like labor. In these contexts, ruling parties armed their allies, providing them with mobilizing structures and political resources that could later be used to challenge the state. Secondly, opposition parties are more likely to maintain their organizational cohesion and the commitment of activists when they use strategies and appeals that escalate conflict and reorient social boundaries around the lines of partisan affiliation. Polarization forges stronger parties, but it also increases the likelihood of violence and authoritarian retrenchment. The book provides an explanation of why democratization in the hybrid regimes of the late Third Wave may prove more conflictual and more protracted than earlier transitions to democracy.