Abstract
The article aims to provide a comprehensive analysis of the impact of decentralisation on regionalist parties’ strength in both national and regional elections. We consider decentralisation both as a putatively crucial event, that is, the creation of an elected regional government, and as a process. Our study is based on a dataset including aggregate vote shares for 227 regionalist parties competing in 329 regions across 18 Western democracies. Our findings show that decentralisation as an event has a strong impact on the number of regionalist parties, as it triggers processes of proliferation and diffusion. Decentralisation as a process has an overall empowerment effect in regional elections, while it does not have an effect in national elections. However, our analysis also reveals that the overall null effect in national elections is actually the result of an empowering effect on new regionalist parties and of an accommodating effect on old regionalist parties.