Russia’s invasion of Ukraine has led to a resurgence of policy attention toward reassurance—an attempt to increase an ally’s feeling of security from external threat. In our recent article, “Trivial Tripwires? Military Capabilities and Alliance Reassurance,” we assess how states can most effectively reassure their allies. We introduce a new typology of reassurance measures based on the interaction of capability and resolve, and test it using case studies and data from original expert surveys. We find that in northeastern Europe, high-resolve signals (for example, tripwire forces) are not viewed as any more reassuring than high-capability, low-resolve signals (for example, forces stationed offshore). Put differently, high resolve cannot offset low capability.

In their thoughtful responses to our piece, James Goldgeier and Lily Wojtowicz, and Oriana Skylar Mastro, respectively, raise important questions about the scope of our findings and identify exciting pathways for future research. Given ongoing security challenges in Europe and East Asia, pursuing these lines of inquiry is critical for both theory and policy, and we believe our typology offers a useful starting point.
Goldgeier and Wojtowicz suggest additional research in three key areas: the role of allies other than the United States in providing reassurance; the different requirements for deterrence and reassurance; and variation in perceptions of reassurance effectiveness across different states. Mastro also suggests further study of three topics: the context-dependent nature of capability; the conceptualization of tripwires; and the reassurance value of transient military operations.

Though the responses raise important questions, we believe our typology still offers useful insights for contexts outside Eastern Europe and hope it sets the foundation for future research.