Reassessing the public goods theory of alliances

The public goods theory of alliances exerts substantial influence on scholarship and policy, especially through its claim that small alliance participants free-ride on larger partners. Prior statistical tests of free-riding suffer from model specification and generalizability problems, however, so there is little reliable and general evidence about this prediction. In this study, I address those limitations with a new test of the free-riding hypothesis. Using data on 204 alliances from 1919 to 2007, I examine how often states with a small share of total GDP in an alliance decrease military spending while states with a large share of allied GDP increase military spending. I find little evidence to support this expression of the free-riding hypothesis. This implies that free-riding based on economic weight is unusual in alliance politics, which may be due to limits on alliance security as a public good or bargaining between alliance members.