High, Dry and Allied: The Ethics of Breaching the Collective Defence Duty

This article adopts a normative approach to one of the most consequential issues of alliance management: the question of if and when an ally is justified in breaching its collective defence duty (CDD). An ally’s CDD constitutes its formal obligation to militarily defend its ally in the event that the latter experiences an armed attack. Drawing on both normative political theory and contemporary International Relations scholarship on alliance credibility and security dilemmas, the article first considers and rejects two opposing but equally extreme views on this question. Next, the article proposes what it calls the Moderate View as a more persuasive response. The Moderate View draws on Glenn Snyder’s concept of the alliance security dilemma to argue that Ally X is justified in breaching its CDD if it is reasonable for Ally X to believe that there is a high likelihood of its imminent entrapment by Ally Y, and if Ally X cannot reduce this likelihood by signalling its concerns to Ally Y. Two distinct arguments are then provided in support of the Moderate View. In the final section, the Moderate View is defended against three objections. The article demonstrates how empirical concepts from IR can inform normative theorising while providing practical ethical guidance for alliance policymakers.