Colonialism is the policy of a country seeking to extend or retain its authority over other people or territories, generally with the aim of economic dominance. In the process of colonisation, colonisers may impose their religion, language, economics, and other cultural practices on indigenous peoples. The foreign administrators rule the territory in pursuit of their interests, seeking to benefit from the colonised region's people and resources.
Colonialism is strongly associated with the European colonial period starting with the 15th century when some European states established colonising empires. At first, European colonising countries followed policies of mercantilism, aiming to strengthen the home-country economy, so agreements usually restricted the colonies to trading only with the metropole (mother country). By the mid-19th century, however, the British Empire gave up mercantilism and trade restrictions and adopted the principle of free trade, with few restrictions or tariffs. Christian missionaries were active in practically all of the European-controlled colonies because the metropoles were Christian. Historian Philip Hoffman calculated that by 1800, before the Industrial Revolution, Europeans already controlled at least 35% of the globe, and by 1914, they had gained control of 84% of the globe.
In the aftermath of World War II colonial powers were forced to retreat between 1945–1975, when nearly all colonies gained independence, entering into changed colonial, so-called postcolonial and neocolonialist relations. Postcolonialism and neocolonialism has continued or shifted relations and ideologies of colonialism, justifying its continuation with concepts such as development and new frontiers, as in exploring outer space for colonization.