This work was carried out with the purpose of establishing the reasons why the United States are strengthening political-strategic cooperation with its partners in APEC s ambit, which was originally an initiative mainly of economic cooperation, in the 2000s, using Joseph Grieco s defensive neo-realism (1997) as the theoretical instrument, primarily the premise that international organizations and agreements are a way for the great powers to rationalize and legitimize its dominance in a region. It was my objective to verify if the hypothesis that the alteration of Asia-Pacific s regional arrangement in an environment of international anarchy, thereby jeopardizing Washington s position caused this change of USA s behavior was right. Due to the context of terrorism dissemination after 09/11, the more aggressive action of paria-states, and the rise of China as a regional power, USA, as a rational actor, are now utilizing this regional integration agreement as a way to increase its influence and power in that region, according to a behavioral pattern already seen in other instances.