This article explores how variations in party systems shape the intensity of insurgency against national authorities in nineteenth-century Latin America. I argue that, under certain conditions, two-party systems may polarize and lead to intense insurgency because they simplify the process of blame attribution, encourage the incumbent party to exclude its opponent from power positions, and motivate leaders to emphasize extreme ideological positions. Conversely, multiparty systems may encourage flexible electoral and congressional alliances among parties, resulting in lower insurgency. I test the argument in four nineteenth-century Latin American republics with different insurgency levels. While in Colombia and Uruguay two-party systems polarized and fueled intense insurgency across the century, Chile and Costa Rica developed flexible multiparty systems that prevented polarization and favored low insurgency.