The Korean Peninsula, surrounded by four major powers (the United States, China, Japan and Russia,) is inherently vulnerable to drastic changes in the Northeast Asian security environment. This security environment has undergone significant changes in the 66 years since the Korean War. Growing North Korean threats requires the ROK to find an effective way to deter North Korea. The collective security system which has guaranteed and organized peace and stability around the world is a reasonable option for the ROK’s security. This paper focuses on international cooperation for the peaceful unification of the Korean Peninsula. It explores the role of the United Nations. The UN should take an active role in increasing peace and stability on the Korean Peninsula by offering a high level of policy coordination, close communication, and diplomatic synchronization. Furthermore, the ROK must request international support for the unification process. For example, the UN could organize a Special Committee for the Normalization of the Korean Armistice for normalization of the armistice regime in the peninsula. Even though peaceful unification on the Peninsula faces significant challenges including power struggles among major states, it is possible if the international community through highly organized institutions plays an active role supporting the two Koreas. These actions should be based on a strong ROK-US alliance. Alliances and a cooperative security system are not mutually exclusive options.