This paper addresses the U.S.-South Korea alliance in the context of Asia’s evolving security architecture. At the crux of the issue is the Biden administration’s desire to uphold the rules-based international order by reinforcing the network of inter-Asia alliances and multilateral institutions, on one hand, and the Moon government’s relative reluctance to deepen and expand security ties linked to an Indo-Pacific strategy that counter-balances China, on the other hand. Leveraging the existing alliance relationship, the Biden administration should encourage Seoul to coordinate with other like-minded countries committed to sustaining a rules-based regional order while assisting Seoul in mitigating potential strategic vulnerabilities. Conversely, as a middle power, South Korea must not shy away from the region’s security architecture, but instead actively coordinate with other actors in shaping the region’s strategic environment. By working in concert with other countries in the Indo-Pacific, Seoul can reduce its geopolitical vulnerability while advancing its national and regional interests.