imperialist (n.)

c. 1600, "an adherent of an emperor or the imperial cause," such as the emperor of Germany (in the Thirty Years War), 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.