Outsourcing Security: Alliance Portfolio Size, Capability, and Reliability

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.联盟组合（alliance portfolios）的过度扩张，会削弱国家的整体安全。出于对联盟抛弃的担忧，国家有动机扩大自身联盟组合的规模与盟友的实力，以确保在冲突爆发时能够获得充足的援助。然而，随着联盟组合规模愈发庞大、整体实力愈发强劲，每个盟友介入冲突的动机——即其预期回报——会逐步降低。在此类情境中，国家为解决联盟抛弃问题所付出的努力，反而可能加剧这一困境。本研究针对联盟组合的规模与实力对冲突介入行为的影响提出相关假设并开展检验。分析结果表明，国家需先达到一定的军事能力最低阈值，此时扩张联盟组合才会提升盟友介入冲突的可能性。此外，国家还需审慎考量自身实力与联盟组合整体实力的相对关系。研究显示，国家通过联盟可额外获取约相当于自身1.5倍的实力，若继续扩张联盟组合，反而会降低盟友介入冲突的概率。