NATO Security Burden Sharing, 1991–2020

In contrast to much of the extant literature, the paper devises a composite security burden measure for the NATO alliance that accounts for three different contributions by allies to their collective security: namely, military expenditure (ME), foreign assistance, and UN peacekeeping spending. Generally, NATO defense burden sharing and free riding are judged solely based on ME even though foreign assistance and peacekeeping promote world prosperity, stabilize regimes, and quell conflicts that affect NATO’s collective security. Our parametric tests for free riding apply a spatial-lag panel model, which addresses the interdependency issues, to a broader security-spending measure that accounts for allies’ membership, contiguity, and inverse distance. In all spatial models, we uncover robust evidence of free riding where allies decrease their aggregate security spending in response to increases in the collective security spending of other allies. We apply a panel generalized method of moments (GMM) estimator to adjust for endogeneity concerns.