This study focuses on the phenomenon that the U.S.-Korea-Japan security triangle wasn’t reinforced but rather relaxed in the intensified competition between the U.S. and China from 2017 to 2022. This article argues that conflicting strategic interests between Korea and Japan are the primary driver of their conflict within the triangular system. Since the Cold War, Japan has maintained dominance in Korea-Japan relations, characterized by an asymmetrical dynamic between the prosperous democratic Japan and the impoverished authoritarian Korea. Furthermore, the article contends that the rise of Korea’s national power and the consolidation of its democratic values have prompted the Moon Jaein Government to seek a recalibration of the Korea-Japan relationship. Korea aims to establish a new type of relationship that is in line with its own strategic interests and democratic values, leading to a contradiction with Japan’s strategic objectives. For instance, the difference in economies between Korea and Japan was 30:1 at the early stage of the U.S.-Korea- Japan security triangle in the 1960s, but in the 2010s, the difference was just 3:1. Even though the economic dimension of Japan still seems superior to that of Korea, Korea has almost caught up with or exceeded Japan in such areas as national defense, foreign trade, global supply networks and democracy. Therefore, the asymmetric relation is in its final stage. However, when faced with the situation in which the security threats of North Korea’s nuclear development and China’s rise in terms of military power increased in the 2010s, both Korea and Japan failed to adjust their mutual obligations and security interests in the symmetric relation, and the U.S. reinforced the U.S.-Korea-Japan security triangle by focusing on the strategic interests of the U.S.-Japan alliance. Thus, Korea faced the
dilemma of entrapment. For these reasons, after the inauguration of the Moon Jae-in Government, Korea had to adopt a passive attitude in the security triangle. As a result, South Korea volunteered to be an arbitrator between the U.S. and North Korea to pursue a solution to the North Korean nuclear problem through diplomatic negotiations, and Korea cooperated with the U.S. in checking China within the framework of the Korea–U.S. alliance.