What Do Empires Do? by Michael Parenti* http://www.voltairenet.org/article165118.html

But I define imperialism as follows: the process whereby the dominant investor interests in one country bring to bear their economic and military power upon another nation or region in order to expropriate its land, labor, natural resources, capital, and markets-in such a manner as to enrich the investor interests. In a word, empires do not just pursue "power for power’s sake." There are real and enormous material interests at stake, fortunes to be made many times over.

So for centuries the ruling interests of Western Europe and later on North America and Japan went forth with their financiers---and when necessary their armies---to lay claim to most of planet Earth, including the labor of indigenous peoples, their markets, their incomes (through colonial taxation or debt control or other means), and the abundant treasures of their lands: their gold, silver, diamonds, copper, rum, molasses, hemp, flax, ebony, timber, sugar, tobacco, ivory, iron, tin, nickel, coal, cotton, corn, and more recently: uranium, manganese, titanium, bauxite, oil, and—say it again—oil. (Hardly a complete listing.)