Reassuring allies in times of crisis: assessing the effectiveness of tools for alliance reassurance in crises

What military and diplomatic instruments are effective for the United States to reassure its allies that their security will be protected as promised? Despite its importance for alliance management, our understanding of alliance reassurance remains incomplete. Specifically, existing research rarely uses direct measures of reassurance outcomes, and pays limited attention to exploring the effectiveness of different toolkits for alliance reassurance. Using a survey experiment with South Korean citizens, this paper examines the effectiveness of a range of military and diplomatic toolkits for reassuring US allies during foreign policy crises. The results demonstrate that conventional and nuclear signals, as well as diplomatic statements of support, significantly assuage the security concerns of South Korean citizens by increasing the perceived safety of South Korea from North Korean military aggression. However, Washington’s diplomatic proposals toward North Korea do not produce similar effects. These findings have implications for debates on interstate signaling and alliance management.