Imperialism was a
policy actively practiced by many
Western powers over much of the past 500 years. It is the
aggressive expansion of an
empire by
annexation or military
subjugation, and the following
economic leeching of those
colonial economies for the
benefit of the "
mother nation".
Often done under the guise of taming the godless heathen populations the "pagan" barbarian cultures, the perpetrators of this policy act like Christian heroes, claiming to liberate the savages from their miserable lives and enlighten them with the knowledge of the "one true God", while themselves committing one of the seven deadly sins, greed. Hypocrisy seems to be easily ignored when profits are being made.
Imperialism pretty much died out after World War II when the balance of power shifted from the traditional Western nations to America and the USSR. Instead of sucking their subjugates dry, they used them as satellite nations instead, helping them in the Cold War.
Marxist theory often dictates imperialism as a natural development of capitalism, and this line of thought was picked up by modern Marxists and socialists, who now accuse globalization of the economy as "imperialist". The broadened generalizations these people make often serve to confuse the issue and is mostly just slander against business.