Stability and resilience of alliances: A network approach

Public-goods models of alliances examine the trade-off between the benefits of a collectively provided good and the private costs of contribution. This line of inquiry prompts a further question: what makes alliances endure? We contribute by characterizing alliance stability and resilience using graph-theoretic concepts, offering a structural explanation for why some alliances persist while others do not. Our framework embeds alliances in node- and edge-weighted networks: links among allies generate positive externalities, whereas links between allies and adversaries capture negative externalities. We relate the resilience of alliances – and of their members – to the members’ core numbers within the alliance-induced subnetwork. We then analyze strategic stability when members choose the magnitude of the externalities through costly contributions and the redistribution of spillovers. Finally, we apply the framework to assess the resilience and stability of the North Atlantic Alliance. • Allies and their adversaries are embedded in a node- and edge- weighted network. • We relate the resilience and stability of alliances to graph-theoretical concepts. • We define two alliance stability concepts and link them to the network’s topology. • We evaluate NATO’s stability, resilience, and measures designed to strengthen it.