Marriages of convenience: explaining party mergers in Europe

While party mergers can have important implications for the development of party systems, their causes have not been studied in a large-n comparative study. Using a new data set that covers 24 European democracies in the postwar period, this study shows that parties merge to overcome electoral thresholds or to form one of the two or three largest parties with an important role in the formation of government coalitions. However, mergers are not motivated by the goal to establish a majority, strongly dominant or largest party. The costs of mergers include ideological differences and various transaction costs related to reaching and implementing merger agreements. These transaction costs are lower if parties previously cooperated and if the partisanship of their voters is low