World War I thumb|right|Belgo-Congolese troops of the Force Publique after the Battle of Tabora, 19 September 1916 Rubber had long been the main export of the Belgian Congo, but its importance fell in the early 20th century from 77% of exports (by value) to only 15% as British colonies in Southeast Asia like British Malaya began to farm rubber. New resources were exploited, especially copper mining in Katanga province. The Belgian-owned Union Minière du Haut-Katanga, which would come to dominate copper mining, used a direct rail line to the sea at Beira. World War I increased demand for copper, and production soared from 997 tons in 1911 to 27,462 tons in 1917, then fell off to 19,000 tons in 1920. Smelters operated at Lubumbashi. Before the war the copper was sold to Germany; but the British purchased all the wartime output, with the revenues going to the Belgian government in exile. Diamond- and gold-mining also expanded during the war. The British firm of Lever Bros. greatly expanded the palm oil business during the war, and output of cocoa, rice and cotton increased. New rail and steamship lines opened to handle the expanded export traffic. During the First World War (1914–1918), the system of "mandatory cultivation" (cultures obligatoires) was introduced, forcing Congolese peasants to grow certain cash crops (cotton, coffee, groundnuts) destined as commodities for export.Mulambu, M. (1974), "Cultures obligatoires et colonisation dans l'ex-Congo belge", In Les Cahiers du CEDAF, 6/7 Territorial administrators and state agronomists had the task of supervising and, if necessary, sanctioning those peasants who evaded the hated mandatory cultivation.Likaka, Osumaka (1997), Rural Society and Cotton in Colonial Zaire, Madison: University of Wisconsin Press.
World War I thumb|right|Belgo-Congolese troops of the Force Publique after the Battle of Tabora, 19 September 1916 Rubber had long been the main export of the Belgian Congo, but its importance fell in the early 20th century from 77% of exports (by value) to only 15% as British colonies in Southeast Asia like British Malaya began to farm rubber. New resources were exploited, especially copper mining in Katanga province. The Belgian-owned Union Minière du Haut-Katanga, which would come to dominate copper mining, used a direct rail line to the sea at Beira. World War I increased demand for copper, and production soared from 997 tons in 1911 to 27,462 tons in 1917, then fell off to 19,000 tons in 1920. Smelters operated at Lubumbashi. Before the war the copper was sold to Germany; but the British purchased all the wartime output, with the revenues going to the Belgian government in exile Diamond- and gold-mining also expanded during the war. The British firm of Lever Bros. greatly expanded the palm oil business during the war, and output of cocoa, rice and cotton increased. New rail and steamship lines opened to handle the expanded export traffic. During the First World War (1914–1918), the system of "mandatory cultivation" (cultures obligatoires) was introduced, forcing Congolese peasants to grow certain cash crops (cotton, coffee, groundnuts) destined as commodities for export.Mulambu, M (1974), "Cultures obligatoires et colonisation dans l'ex-Congo belge", In Les Cahiers du CEDAF, 6/7 Territorial administrators and state agronomists had the task of supervising and, if necessary, sanctioning those peasants who evaded the hated mandatory cultivation.Likaka, Osumaka (1997), Rural Society and Cotton in Colonial Zaire, Madison: University of Wisconsin Press.