In the late 19th century, Imperial Germany conquered the regions that are now Tanzania (minus Zanzibar), Rwanda, and Burundi, and incorporated them into German East Africa. During World War I, an invasion attempt by the British was thwarted by German General Paul von Lettow-Vorbeck, who then mounted a drawn out guerrilla campaign against the British. The post?orld War I accords and the League of Nations charter designated the area a British Mandate, except for a small area in the northwest, which was ceded to Belgium and later became Rwanda and Burundi.