Security, autonomy and defense burdens: The effects of alliance membership in the 19th and 20th centuries

This paper investigates the effect of alliance membership on the defense burdens of major powers in the 19th and 20th centuries. We hypothesize that the reactions of states to alliance membership will be different in the pre-nuclear and nuclear eras. Possession of nuclear weapons by allies makes the security provided by the alliance more akin to a collective good than is the case in the pre-nuclear era. States join alliances for two reasons: security and autonomy. The effects of each of these concerns are identified. We include in our model such alliance-level factors as the power equivalence of the allies and the number of states in the alliance. We also look at state-level variables such as power position within the alliance. We conclude that the nuclear period generally operates as the free-rider principle would posit, while models based on “complementarity of effort” are more applicable in the earlier period.