This dissertation addresses two important questions: what constitutes regionalist party success and what factors explain this success? Regionalist parties are political parties that compete within a confined geographic region and focus on gaining greater political autonomy. This differentiates them from mainstream parties who prefer to emphasize traditional left-right political issues and compete across the entire country. I argue that to better understand the electoral outcomes of these parties, their results need a more nuanced categorization: breakthrough, failure, and persistence. Breakthrough occurs when a party has a large surge in support. Electoral failure happens when a party suffers a precipitous decline in vote shares, diminishing its political relevance. Persistence results when a party replicates its previous electoral outcome with minimal change. I used a supply-side and demand-side theoretical framing to consider the influences on regionalist party outcomes. Demand-side or “bottom-up” based theories state that political parties are primarily responsive organizations that adapt to changes in public attitudes. Thus, they must respond and closely align with the social, cultural, and economic positions of the public. I hypothesized, however, that supply-side factors best explain a regionalist party’s fate. Supply-side or “top-down” theories maintain factors outside of public demand can shape elections. These include institutional arrangements and party strategies, such as the positions the parties take and salience they give to particular issues. In this framework, the choices parties make can impact citizens’ voting. To explain breakthrough, failure, and persistence, I found three factors most relevant: the emphasis mainstream parties put on issues related to regional autonomy compared to left-right issues, the positions mainstream parties take on decentralizing power, and the positions that regionalist parties adopt regarding regional autonomy. When all of these align favorably in an election a party is more likely to breakthrough. In instances where all of them align unfavorably the probability of failure increases. Persistence is most probable when one or two of the factors is beneficial, but not all of them. I analyzed these questions using a mixed-methods approach that included multiple regression analyses and case studies of eight different elections in Scotland.

Increasing calls for regional independence are being made in several European countries, and such calls are accompanied by growing public support for secessionism. Over the last decade, Catalonia and Scotland have enjoyed the highest level of political mobilization for secession in the European Union. This research highlights the role of the media in changing attitudes toward independence and studies regionalist parties' strategic choices to understand their electoral success at the regional elections at a time of fast growth of independence sentiments among the population. This study employs different methods: process tracing to focus on the specificities of the independence process in a view to understand how the secessionist agenda transformed the cases; frame analysis of media links the theoretical arguments and their representation in the public discourse; content analysis of regional parties’ electoral programs via Regional Manifesto Project approach helps to define the strategic choices of regionalist parties which brought success to their secessionist agenda at the regional elections; most-similar cases comparative analysis allows to identify commonality and differences between the cases of Catalonia and Scotland. This dissertation uncovers how: the media communicate regionalist arguments to the audience; the media justify independence claims; regionalist parties strategize their secessionist programs. First, a strong pro-region bias is the main feature of media coverage. Secondly, saliency in influenced by the political process as a largely exogeneous factor, but the framing process may also influence reality by giving particular meaning to the major political events and by framing them as political opportunities or as having transformative power. Third, the political competition structure contributes to the strategic choices of political parties. My research contributes to the framing literature by considering the role of diagnosis, prognostic, and motivational framing in the independence discourse. It highlights the extent of pro-region message flows vis-à-vis pro-center and neutral messages in media communication. My analysis contributes to previous research on regionalist parties by making an in-depth case study to differentiate between subsuming and blurring strategies adopted by secessionist actors.