Imperialism (Civ5)/Civilopedia

In its most basic form, Imperialism describes an unequal relationship between one nation and another, where the former has some amount of control over the latter country-usually in the form of some kind of empire. Imperialistic dynasties can be found in all the histories of the world, from China to Rome to Britain, and imperialism as a concept has existed for thousands of years, just about as long as governments in general. The term "imperialism," however, wasn't coined until the 16th century, where it was used to describe the foreign policies and proceedings of nations like Spain, Britain, Belgium, and the Netherlands, as they swiftly built up imperial ties with the Americas, Africa, and Asia.
While Imperialism is traditionally connected with the large, iconic, militaristic empire, it can be exhibited in a much more subtle manner. Formal control of the weaker state’s government isn't always necessary, and a stronger civilization will sometimes control a weaker one purely through indirect economic, political or religious means.