Clubs of Clubs: Fragmentation in the Network of Intergovernmental Organizations

Has international cooperation become fragmented in recent decades? We focus on a specific form of potential fragmentation in the international system: the extent to which the network of intergovernmental organizations (IGOs) consists of distinct clusters of closely cooperating states. IR scholars—including those with an interest in the causes and consequences of membership in IGOs—pay relatively little attention to the structure of the larger IGO network. At the same time, scholars concerned with fragmentation often assume that it has increased without clear measures of this phenomenon. We use the network analytic technique of modularity maximization to show that throughout the post–World War II period, the structure of the IGO network can generally be divided into distinct groups of states on the basis of their shared IGO memberships. Yet we also show that temporal trends indicate that the IGO network has become less fragmented in recent decades, suggesting that cooperation via these organizations has become more global and less regional. Our findings indicate that, at least as far as cooperation through formal organizations is concerned, fragmentation has decreased in recent decades.