Hegemony
In the 19th century, hegemony came to denote the "Social or cultural predominance or ascendancy; predominance by one group within a society or milieu". Later, it could be used to mean "a group or regime which exerts undue influence within a society". Also, it could be used for the geopolitical and the cultural predominance of one country over others, from which was derived "hegemonism", as in the idea that the Great Powers meant to establish European hegemony over Asia and Africa.
Posthegemony
In international relations, "posthegemony" refers to the decline of the US unilateral hegemony. This has likely been the result of the difficulties that have arisen out of the unilateral style foreign policy. These difficulties predominantly include disdain from; those directly affected by the, sometimes forceful, hegemonic actions of the US, those who spectated the actions, and even Americans themselves who view the actions of their government as immoral. For example, after the Vietnam War, in 1978, 72 per cent of Americans thought the war was not a mistake but fundamentally wrong and immoral. This exemplifies the hegemonic decline: how could the US maintain the legitimacy of their interventions if their own citizens find them wrong and immoral?