A general equilibrium model of multi-party competition

The paper introduces a generalized spatial model that is motivated by the frequent changes in party identity and electoral laws that characterize transitional party systems. In this model, parties may (1) change their platforms, (2) their identities through coalitions and splits and (3) if they form a winning coalition, the electoral law. The equilibrium is defined as a state such that no party or coalition can strictly benefit from changing the electoral law, its platform, or from splitting or coalescing. The results show that while there are games with no institutional or coalitional-split equilibria, such equilibria do exist under relatively undemanding conditions. The main finding is that once an institutional and identity equilibrium is achieved, it is generically robust against small trembles in party platforms or voter preferences. This robustness facilitates greater stability in terms of institutions and party identities in mature party systems where such trembles are smaller than in transitional systems.