Kosovo is a watershed in the World Politics. As an ethnic phenomenon, it not only prompted a reexamination of some of the central issues of ethnicity but also raised an important question about the role of United Nations in international politics. This study, by discussing the theoretical issues involved in ethnic phenomena, analyse various questions raised by NATO's attack on the former Yugoslavia. These questions involved the issues of humanitarian intervention, the diminished relevance of the United Nations in the sphere of the use of force in world affairs, changed peace-keeping role of the United Nations in intra-state conflicts, the United States' role as a sole super power conflicts and its impact on the United Nations system.