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Outsourcing Security: Alliance Portfolio Size, Capability, and Reliability


  • A previous iteration of this research was presented at the 2009 annual meeting of the International Studies Association. I am indebted to Ryan Baird, Bill Dixon, John Doces, Gary Goertz, Glenn Palmer, Tom Volgy, the editors of ISQ, and two anonymous reviewers for their invaluable comments and suggestions. Data and code to replicate this analysis are available via the ISQ data archive.


Grant, Keith A. (2012) Outsourcing Security: Alliance Portfolio Size, Capability, and Reliability. International Studies Quarterly, doi: 10.1111/isqu.12021
© 2012 International Studies Association

The overexpansion of alliance portfolios can diminish the overall security of states. Due to the fear of abandonment, states have an interest in expanding the size and capabilities of their alliance portfolio to ensure the receipt of adequate assistance in the event of a conflict. However, each ally’s incentive to intervene—their expected reward—decreases as alliance portfolios become larger and more powerful. In such situations, states’ efforts to address the alliance abandonment problem may serve to exacerbate it. Hypotheses regarding the influence of alliance portfolio size and capabilities on conflict intervention are tested. Analysis suggests that states must possess some minimal threshold of military capability before an expanded alliance portfolio increases the likelihood of intervention in conflict. Furthermore, states must be mindful of their individual capabilities relative to those of their collective alliance portfolio. States appear capable of adding roughly 1.5 times their own capability through alliances before additional expansion actually decreases the probability of intervention.