One Radical, Not Many: Party System Institutionalization and the Type and Number of Populist Parties

This article examines how party system structure shapes the type and number of populist parties in Europe. It investigates why some party systems generate radical populist parties while others produce alternative populist forms, and why the number of populist competitors varies across elections. Drawing on Sartori’s theory of party system dynamics and the political opportunity structure framework, this article studies fragmentation, polarization, and party system institutionalization as conditions for populist parties’ strategic incentives. Using a dataset of 369 populist party observations across 25 European countries (2000–2024), the analysis employs Firth logistic regression to model populist type and Poisson regression to model populist multiplicity. The findings reveal that more institutionalized systems are more likely to generate successful radical populist parties and simultaneously host fewer populist competitors. While less institutionalized systems are humus for many populist parties and different types.