Keeping Parties Together: Party Discipline, Party Policy Positioning, and Party Splits


Party Unity is an important feature of the political landscape. How and to what extend does individual members within a political party choose to make contributions to the collective outcome of their party is key to understanding party unity. I highlight the importance of intra-party politics and argue that the rank-and-file support is essential for the security and influence of party leaders. When decisions to support current party leaders are a function of the level of party discipline and tolerance for policy among individual members, the existence of viable outside options create incentives for individual faction members to leave the established party, thus leaving the party to members holding similar preferences. I formalize this argument in a game-theoretic model and test it empirically using the party-positioning data drawn from comparative election manifestos, legislative roll-call voting records, and an originally collected data of party splits in democratic countries during the period 1945-2001.