Populist electoral success and party system concentration: A cross-national analysis

Why does the electoral success of anti-establishment populist movements lead to fewer, rather than more, effective political parties? Using panel data from electoral democracies worldwide (1970–2020), we document a robust negative relationship between populist electoral success and subsequent party system fragmentation. We theorize that the electoral validation of populism triggers three mechanisms that concentrate party systems: delegitimation of moderate positions, polarization that eliminates centrist parties, and the establishment of barriers preventing new challengers from entering. Employing entropy-balanced two-way fixed effects, we find that a one unit increase in our Vote-Weighted Populism Index reduces the effective number of parties by 0.388 units. This effect persists across diverse institutional contexts, though regional analysis reveals important variation: the concentration effect is strongest in Europe and Asia-Pacific, and null in Latin America and Sub-Saharan Africa. In terms of moderation, we demonstrate that economic recessions amplify the effect, nearly doubling its magnitude, while other institutional factors seem to play no significant role.