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Explaining the Breakdown of Dominant Party Systems: Party Splits and the Mechanisms of Factional Bargaining

Abstract This paper presents an explanation for the breakdown of dominant party systems. In contrast to previous works that examine how ruling parties lose their dominant position as a result of interparty competition, this paper focuses on how they are undermined from within by factional conflict. Through an overview of dominant party systems in the postwar world, we show that most of the ruling parties suffered from major splits that significantly reduced their electoral strengths before their final electoral defeat. In order to explain why large groups of politicians decide to leave dominant parties that are likely to remain in power, we develop simple game-theoretic models of intraparty bargaining between party factions over the distribution of benefits from office. Our results suggest two mechanisms through which dominant parties break up. First, factional defections from dominant parties are likely to occur when they are experiencing a significant decline in public support. Second, factional defections are likely to occur when a non-mainstream faction is rapidly losing its bargaining power against the party leadership. Importantly, our results show that under certain conditions, dominant parties will break up even when their electoral prospects are much better than the opposition. We briefly discuss how these mechanisms can be applied to actual cases of dominant party systems.