As the core of the US-ROK alliance, the US Forces in Korea (USFK) has been playing various military and political roles. Contrary to the importance of its role, the number of forces has been consistently reduced. This study aims to explore the root cause of this seemingly contradictory phenomenon through the case of Nixon Administration’s troop withdrawal policy from South Korea, which was an important test case of the Nixon Doctrine’s core tenet, “reducing military engagement while maintaining political influence.” With this aim, the study presents several findings and arguments. First, the longevity of the USFK can be explained primarily in the context of the U.S. hegemonic stability. Second, the U.S. excessive military commitments to the defense of South Korea and concerns about ‘entrapment’ in the war were important factors in the continued reduction. Third, a certain amount of military presence was necessary since the various political roles of the USFK are essential to maintaining stability in the region. In sum, the continuation and reduction of the USFK can be understood in the context of the hegemonic stability of the U.S. global and regional strategy, which has been supported by a combination of the political and military role of the USFK in Northeast Asia.