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 colony 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.