For the computer game, see Imperialism (video game).
It is simply one country or power taking over and imposing its form of government and/or culture over another.
Territories that have been, at one time or another, part of the British EmpireImperialism, defined by The Dictionary of Human Geography, is "the creation and maintenance of an unequal economic, cultural and territorial relationship, usually between states and often in the form of an empire, based on domination and subordination." Imperialism has been described as a primarily western concept that employs "expansionist – mercantilist and latterly communist – systems."
Imperialism is considered the control by one state of other territories. Through political or military means (direct imperialism), the imperial power may take over the government of a particular territory, or through economic processes (indirect imperialism), in which the concerned region is officially self-governing but linked to the imperial power by (often unequal) trade relations. Furthermore, the notion of cultural imperialism is indicated by "existing or traditional ways of life and ways of thinking [that] are subordinated to the culture of the imperialists."