Self Enforcing Voting in International Organizations

Some international organizations are governed by unanimity rule, some others by a majority system. Still others have moved from one system to the other over time. The existing voting models, which generally assume that decisions made by voting are perfectly enforceable, have a difficult time explaining the observed variation in governance mode, and in particular the widespread occurrence of the unanimity system. We present a model whose main departure from standard voting models is that there is no external enforcement mechanism: each country is sovereign and cannot be forced to follow the collective decision, or in other words, the voting system must be self-enforcing. The model yields unanimity as the optimal system for a wide range of parameters, and delivers rich predictions on the variation in the mode of governance, both across organizations and over time.