With the end of the Cold War and the colapse of the Soviet Union, new systemic pressures emerged, demanding the US a leading position in the international arena, as well as encouraging a change in the political and economic behavior towards its former enemy. Thus, the purpose of this thesis consists in the analysis and explanation of the new cooperative attitude adopted by the Americans regarding to the Russians, based on perceptions, which consequently turned into actions, of their decision makers. In turn, the hypothesis to be verified in this work is based on the fact that the greater the gap between U.S. and Russia in the first ten years following the Cold War, and the greater the perceptions of American leaders about the hegemony of their country in the political and economic realm, the greater U.S. tendency of adopting a less aggressive and hostile but more friendly behavior towards Russia.