With the collapse of former Soviet Union, while bipolar international system lost its validity, intellectual debate about possible structure of new international system emerged. At these debates, scholars stressed the US’s absolute superiority, lack of capability of other great powers that possibly would balance existing US power and establishment of unipolar international system under the US hegemony. But in the course of time the concerns about the system moved from unipolarity to multipolarity, because the 2003 Iraqi operation has weakened the US’s economic and military power capabilities. Separately Russia, China, and the European Union do not fulfill all requirements of being a great power mentioned by the structural realism, such as having great military, economic and political capabilities, pursuing global policies, and ability of changing attitudes of their allies. While the United States still supports unipolar structure, Russia, China and the European Union prefer to see establishment of multipolar one. At the end it is possible to see that in the post – Cold era a multipolar structure with several regional centers will be formed and the relations among the actors will be loose rather than tight ones.