The development of the concept of the Indo-Pacific strategy, since its adoption by the United States in 2017, has primarily been driven by the emergence of China as an object of strategic concern and a perceived threat in the United States and South Korea. The main impacts of a rising Chinese threat are potentially to overshadow and distract from—but not abandon—the U.S.-South Korea alliance prioritization of North Korea as the primary focus and main object it has defended against. A potential secondary impact may be to heighten the inclination on the part of U.S. and South Korean policymakers to subordinate policy toward North Korea to policy toward China as an instrument designed to force China to take responsibility for managing the North Korean threat. This article outlines the evolution in perceptions of each of the three main actors in the U.S.-South Korea-North Korea triangular relationship, both with reference to their perceptions and approaches to each other and to the evolution and implications of their respective interactions with China. In addition, it analyzes the main features and impacts of the emergence of U.S.-China rivalries on the postures and priorities of the United States, South Korea, and North Korea. Finally, it draws conclusions regarding the future of the U.S.-South Korea-North Korea triangular relationship against the backdrop of China’s rising power and U.S.-China rivalry, as well as the strengthening prominence of the U.S.-Japan-South Korea and China-North Korea-Russia triangles.