Political map of Sub-Saharan Africa 15 October 1917 (Conquest of German East Africa): By the beginning of 1917 the Allies had confined the German forces in East Africa to the bush country south of the Rufiji River (East African Campaign (World War I)). The British crossed the Rufiji in January but, plagued by supply problems and unable to match the generalship of the German commander Paul von Lettow-Vorbeck, took until November to complete the conquest.