Replication Data for: Free Riding, Network Effects, and Burden Sharing in Defense Cooperation Networks

How do states distribute the burdens of collective defense? This paper develops a network theory of burden sharing. We focus on bilateral defense cooperation agreements (DCAs), which promote cooperation in a variety of defense, military, and security issue-areas. Using a computational model, we show that the amount of effort that DCA partners expend on defense depends on the network structure of their agreements. In bilateral terms, DCAs increase defense spending by committing states to defense activities and allowing partners to reciprocally punish free riding. However, as a state's local network of defense partnerships grows more densely connected, with high levels of transitive "friend of a friend" relations, DCAs have the countervailing effect of reducing defense spending. The more deeply integrated states are in bilateral defense networks, the less they spend on defense. We distinguish two potential mechanisms behind this effect -- one based on efficiency improvements, the other on free riding. An empirical analysis using multilevel inferential network models finds stronger support for efficiency than free riding. Defense networks not only reduce defense spending, but they do so by allowing countries to produce security more efficiently.