When do external threats strengthen security community cohesion, and when do they produce fragmentation? Security community theory has generated substantial insight into how communities form and maintain peaceful relations among members but has largely neglected how communities respond to external existential threats. This paper addresses this gap by developing a conditional theory of security community resilience specifying three scope conditions that determine whether external challenges reinforce or undermine collective solidarity: threat framing congruence with constitutive values, institutional activation capacity enabling coordinated response, and burden distribution legitimacy sustaining member commitment. The theory is tested through structured comparison using NATO (North Atlantic Treaty Organization) as the primary case. Temporal comparison of NATOs responses to Russian aggression in 2014 versus 2022 demonstrates that variation in scope conditions rather than threat magnitude accounts for divergent outcomes. Cross-alliance comparison with SEATO (Southeast Asia Treaty Organization) and CENTO (Central Treaty Organization) shows that security community characteristics distinguish successful from failed alliance responses. Intra-alliance comparison reveals that differential identity alignment, framing resonance, and burden-sharing acceptance correlate systematically with member state commitment variation. Process tracing of three key decisions — NSATU (NATO Security Assistance and Training for Ukraine) establishment, Swedish accession negotiations, and burden-sharing transformation — reveals the pathways through which theorized mechanisms operated. The analysis demonstrates that the three scope conditions account for variation that alternative explanations — including pure threat response, hegemonic imposition, or material capability aggregation — cannot adequately explain. The framework generates falsifiable predictions about conditions under which NATOs resilience will persist or erode, providing both scholarly insight and practical guidance for maintaining alliance cohesion in an era of great power competition.
Guy-Maurille Massamba (Tue,) studied this question.