This article explores ways to strengthen the ROK-U.S. alliance under Biden administration, based on the concept of strategic integration. Strategic integration and disintegration between two countries is determined depending on how the great power’s grand strategy and the client ally’s military vulnerability are combined. During the Trump administration, the ROK-U.S. alliance experienced strategic disintegration caused by disharmony of their alliance from the U.S. buck-passing strategy and ROK’s downplaying the role of alliance. This was particularly related to the U.S.-China relations and North Korean nuclear problem. In contrast, the Biden administration has expressed its willingness to restore and strengthen its alliance network, which is different position from that of Trump administration. On the basis of shared interests and values, the U.S. stresses out the importance of the alliance cooperation. This suggests a possible swift in Americas alliance strategy to direction of balancing. But despite this outlook, to fortify an level of strategic integration in the ROK-U.S. alliance, the U.S. should take much more active interest in North Korea nuclear problem as well as South Korea must pay much more attention to regional diplomatic-security issues beyond the Korean peninsular. This study proposes the Indo-Pacific Strategy of the U.S. and South Korea’s position towards it, with the issue of establishing trilateral cooperation between the U.S., South Korea, and Japan, and the North Korean nuclear problem being the three factors that will determine the level of strategic integration of the ROK-U.S. alliance. Given these challenges, the article proposes proactive participation in the U.S.-led liberal international order, preventing risks created by China-ROK relations, and strengthening cooperation with the U.S. on the goal of North Korea’s denuclearization as strategic options that the South Korean government needs to consider.