This article explores alliance effectiveness with a particular focus on peacetime capability-building activities. Questioning why an alliance succeeds in an effective capability-building activity sometimes but not others, this article argues that the key to effectiveness rests on the civil-military relations of the smaller ally. The military effectiveness of capability-building activities increases if the preferences of civilian and military leaders of the smaller ally are converged. Furthermore, constructive civil-military coordination positively impacts military effectiveness. This article tests these propositions with the FXIII project, which is regarded as the largest fighter jet procurement project of the Republic of Korea (ROK). The military effectiveness of the project declined across two phases, which is attributable primarily to unproductive coordination between civilian and military leaders in phase two. This case study reveals that the impact of preference alignment does not influence military effectiveness as broadly as does civil-military coordination.

Key words: ROK–US alliance, military effectiveness, capability-building activities, civil-military relations, weapons procurement, FX-III project.