Chad Basin
In 1865 to 1867, two German expeditions under Gerhard Rolfs and Gustav Nachtigal explored the Chad Basin and the Mandara Mountains. They noted the potential commercial benefits of the area to Germany. In 1868, Nachtigal returned, reaching Lake Chad basin in June 1870. He stayed three years as a guest of the Sultan of Bornu, noting the groups around and their relations to one another. He returned to Europe in 1875 and published a three-volume "Sahara and Sudan" in 1879.