The Price of Protection: Explaining Success and Failure of US Alliance Burden-Sharing Pressure

Existing scholarship on alliance burden sharing focuses on explaining why smaller allies often undercontribute relative to their larger partners. However, the literature largely neglects the role played by great-power pressure in shaping burden-sharing outcomes. I argue that rather than being a product of rational free riding, allies’ defense efforts are often a response to their patron’s threat of abandonment. When a patron can more credibly threaten to reduce its protection, and when doing so would impose serious costs on allies, the former is better positioned to elicit burden sharing. I test the theory using data on allied burden sharing in US alliances from 1950 to 2010. The results show that allies exhibit higher levels of burden-sharing efforts when they are geographically vulnerable to attack, whereas allies exhibit lower levels of burden sharing when they are in geostrategic locations valuable to the United States.