Alliances as fair-weather friendships : external threats and alliance stability

Abstract

The balance of threat theory argues that alliances form as response to increasing threats and dissolve when threats decline. However, if one alliance member finds itself in a more severe threat environment, how will other alliance members react? Will allies who are not subject to this greater threat strengthen their relations to deter this threat or terminate the alliance to avoid being entangled by unwanted conflicts? I argue that allies perceive external threats differently. It is the relative threat levels among allies and its respective changes that affect alliance stability. I hypothesise that states tend to renege alliance commitments and even terminate the relations when there is greater imbalance of threat levels, measured by Maoz’s strategic reference group (SRG). I test these hypotheses on alliance termination from 1816 to 2016 and the effect of extended deterrence from 1816 to 2010. The empirical results reveal that as the gap of threat levels increases among allies, the alliance agreement is more likely to be violated. Furthermore, the results show that a potential challenger is more likely to initiate a militarized dispute against a target which bears higher level of threats than its allies. The study therefore challenges the conventional assumption of the common perception of external threats and solves the empirical inconsistencies on threat levels and alliance stability.