The Survival and Termination of Party Mergers in Europe

Why do constituent parties that participated in a party merger (that was intended to be permanent) decide to leave the latter to re-enter party competition separately? To address this question, we conceptualize merger termination as an instance of new party formation, as an instance of coalition termination and as an instance of institutionalization failure. Building on this conceptualization, we theorize three sets of factors accounting for which mergers are likely to be terminated by constituent parties and which are not. To test these three sets of hypotheses, we use a mixed methods design. We first apply survival analysis to a new dataset on the performance of mergers in 21 European democracies during the post-war period. Our findings support hypotheses derived from a conception of merger termination as new party formation: pre- and post-merger legislative performance significantly affect the probability of merger termination. Furthermore, the institutionalization of constituent parties helps to sustain mergers if the latter already built trust in pre-merger cooperation, in line with our conception of merger termination as institutionalization failure. We then analyze two theory-confirming case studies, one merger survival and one termination. They not only substantiate the working of the significant variables identified in our large-N analysis that drove our selection of case studies. They also reveal how mediating factors difficult to capture in large-N designs help to account for why factors that – theoretically - should have complicated the working of the ‘survival case’ and been beneficial to the ‘termination case’ did not generate the expected effects.