During the Cold War a balanced peace (between the West and the East) and a hegemonic peace (inside western world) cohabited. Starting from the fall of the bipolar order, U.S. has been proceeding to adapt the working rules of the international political system to the new effective reality. Caused by the disappearance of a credible global challenger, and for the unipolar nature assumed by the distribution of strategic power, American hegemony now witnesses the accentuation of its own imperial mood, even if in some constituzionalized forms. The universal mission of American hegemony - due to the own values of liberal hegemony and market economy, which are also its ideological flags - is becoming more and more evident. The process of progressive self-consciousness of an imperial fate is investigated from the analysis of the evolution of pax americana over the years running from the first Bush presidency to the latter one.