Abstract
The deteriorating European security environment underscores the continuing relevance of NATO’s collective defence commitments. Since NATO is a military alliance comprising 32 electoral democracies, the commitment to defend any member relies on the domestic politics of its members. For these commitments to be credible, the alliance requires domestic political consensus and public support for defending allies that become targets of external aggression. However, NATO’s annual surveys reveal striking cross-national heterogeneity among allied states in public willingness to honour their collective defence commitments under Article 5. Despite the increased interest in examining the microfoundations of alliance politics, we still lack systematic explanations for why the publics in some member states are more hesitant to defend allies than in others. To address this important gap, we will analyse data from a unique multi-year survey conducted on nationally representative samples across all NATO countries. Using multilevel statistical modelling, our study will provide the first evidence on country- and individual-level factors that explain the large cross-national variation in public views on collective defence. Our findings will contribute to scholarly debates on the role of public opinion in military alliances and the pressing policy discussions about NATO’s cohesion and credibility.