Explaining party splits and mergers in Europe

Abstract

This thesis investigates the following research question: what explains party splits and mergers? The thesis argues that splits and mergers necessitate a trade-off between political elites' office and policy or ideological goals. Parties split when political elites expect office gains or when expected office losses are lower than ideological gains. Similarly, parties merge when expected office gains are higher than ideological losses and when the merging parties are able to credibly commit to a merger agreement. These theoretical arguments are tested using statistical analyses of a new dataset recording splits and mergers of the parties with at least 1 percent of vote in 24 European democracies during the post-war period, as well as 11 qualitative case studies. In order to capture more precisely political elites' incentives to split and merge parties, these analyses distinguish between (1) major and minor splits and (2) major and takeover mergers. The size of the splinter faction relative to the parent party is larger in the case of major splits than in the case of minor splits. Major mergers occur when the label of the merged party is different from those of the merging parties, while in the case of takeover mergers the name of the merged party is the same as that of one of the merging parties.