This article explains why, in the wake of South Korea's democratization, the US-Republic of Korea alliance has suffered a steady decline while avoiding an abrupt collapse. The author argues that democratization weakened this asymmetric alliance by increasing the political influence of nationalism in South Korea. New South Korean democratic elites, subscribing to nationalist ideals, demanded an autonomous, equal relationship with the United States regardless of the de facto power disparity between the two countries. These elites also deemphasized the security threat from North Korea—with which they perceived a shared national identity—and adopted an unconditional engagement policy with that nation. The United States, in turn, resented the apparently unrealistic policies of these elites and showed a decreased interest in the alliance. Democratization, however, did not cause an abrupt end to the alliance, for two reasons. First, North Korea's military strength preserved a significant strategic need in South Korea for allied support. Second, as the result of a measured transition process, old pro-alliance elites in South Korea retained enough political clout to proscribe a radical shift in foreign policy away from the alliance with the United States, while new elites had opportunities to reconcile their nationalist ideals with strategic realities.