What word or phrase does your mother always say?
c.1600, "an adherent of an emperor," such as the emperor of Germany, France, China, etc., probably modeled on French impérialiste (early 16c.); from imperial + -ist. The shift in meaning to "advocate of imperialism" (1893) came via the British Empire, which involved a worldwide colonial system. See imperialism. As a term of abuse in communist circles, attested by 1918. As an adjective by 1816.
1826, "advocacy of empire," originally in a Napoleonic context, also of Rome and of British foreign policy, from imperial + -ism. At times in British usage (and briefly in U.S.) with a neutral or positive sense relating to national interests or the spread of the benefits of Western civilization, but from the begining usually more or less a term of reproach. General sense of "one country's rule over another," first recorded 1878. Picked up disparagingly in Communist jargon by 1918.
It is the old story of 1798, when French republicanism sick of its own folly and misdeeds, became metamorphosed into imperialism, and consoled itself for its incapacity to found domestic freedom by putting an iron yoke upon Europe, and covering it with blood and battle-fields. [Francis Lloyd, "St. James's Magazine," January 1842]
Acquisition by a government of other governments or territories, or of economic or cultural power over other nations or territories, often by force. Colonialism is a form of imperialism.