Latest developments in the world have shown that International Organizations (IO) have an important role in mediating conflicts and assisting states in their fight against terrorism. However, there is considerable literature in the field of international relations on the role of IOs and there is a debate as to the effects of IOs over states. While realists argue that states do not matter, liberalists argue that IOs are an important part of international relations. Both arguments hold at different stages of the life cycle of various IOs. In that sense, North Atlantic Treaty Organization (NATO), United Nations (UN) and European Union (EU) have been examined. While establishment of some IOs can be explained by realist explanations, the decision making procedures of some IOs are better explained by liberalist arguments.