International Affair Quarterly,Volume 3, Issue 2, August, 2023 44 EVALUATION OF THE PRINCIPLE OF COLLECTIVE SECURITY IN UNITED NATIONS IN THE POST-COLD WAR ERA. DR. AGABA HALIDU Department of Political Science and International Relations, University of Abuja Email: agaba.halidu@uniabuja.edu.ng Phone: 07049995696 YUSUF A. ADEGBITE Department of Political Science and International Relations, University of Abuja Email: yadecity4all@gmail.com Phone: 08102639442 Abstract The promotion of peace and security in the world necessitates security cooperation between states and collective security remains a way to pursue it. Collective security is one of the most promising approaches for peace and a valuable device for power management on an international scale. Collective security can be understood as a security arrangement, political, regional, or global, in which each state in the system accepts that the security of one is the concern of all, and therefore commits to a collective response to threats and breaches to peace. This paper explored the changed meaning, application, challenges and failure of the concept of collective security within the United Nations (UN) to deal with security concerns within the international system. Since the UN has made clear commitments to collective security. The paper highlighted the tension between the theory and practice of collective security in UN. The theory of collective security itself was adopted in this paper while secondary sources of data were used for descriptive analysis. The paper discovered that the success of collective security depends on a number of strong powers that are willing and able to enforce the norms and rules of collective security. Likewise Collective security is a workable, yet imperfect and unreliable system for vulnerable countries. The paper concluded that what is been practice by UN is “Selective Interest” not “Collective Security”. Consequently, the present structure of Security Council in United Nations and their veto power is a major threat and hindrance to collective security because members with veto power consider their national interest first before collective security. This paper therefore recommends that the Security Council should be restructured to accommodate equal members from all the continents and veto power should be abrogated. Keywords: Collective Security, Selective Interest, United Nations, Alliance, High