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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.
Surdea‐Hernea et al. (Fri,) studied this question.