This dissertation argues that low-level party activists are the primary tool that Latin American political parties use to forge and maintain other voters partisan loyalties. Through their year-round grassroots party work, activists pull their network peers into the party, tailor their party’s image to each community’s particular political tastes, and mediate the flow of political information through their social networks. Consequently, parties are more likely to attract new partisan supporters and hold onto their partisans during moments of crisis in communities where they have a dense network of local activists and strong grassroots party organizations.
I test this argument using a mixed-methods research design that combines historical analyses of the development of parties across the region, field research on contemporary grassroots party activism in Chile and Uruguay, and quantitative analyses based on both historical and contemporary data on local party organizations and mass party identification. Chapters 1 through 3 develop a theoretical framework about the relationship between party leaders, party activists, social networks, and ordinary voters. Chapters 4 through 7 trace the historical development of Latin American parties from the 19th century to the present. These chapters demonstrate that the way that Latin American parties organized themselves at the grassroots level in different periods explains the rise and decline of mass partisanship over the last two centuries and the wide variation in the fates of different parties in each period. Chapters 8 and 9 use spatial analysis and social network analysis to test the effect of party activists on the partisanship of the other voters in their communities.