Google Books has a helpful summary:

On 12 May 1883, the German flag was raised on the coast of South-West Africa, modern Namibia. As settlers began to take over the tribal lands of the indigenous peoples, the Herero and Nama resisted and Germany launched a war of extermination. It ended with the construction of concentration camps, in which prisoners were systematically worked and starved to death. Years later, the soldiers and bureaucrats who had administered the camps, and the racial theories that had inspired them, would play a role in the formation of Nazism. David Olusoga and Casper W. Erichsen have uncovered extraordinary links between the Nazis and the atrocities committed in Africa under Kaiser Wilhelm. The infamous brown shirts worn by the Nazi storm troopers were colonial uniforms, originally designed as camouflage for the desert sand. The memory of Germany's African empire was revived as inspiration for the Nazi's wartime empire in the European East. Using shocking new archival evidence, The Kaiser's Holocaust is the definitive account of a genocide that was deliberately concealed for a century - a history that modern Germany has not yet come to terms with. Today, as the graves of the victims are uncovered in the Namibian deserts, the re-emergence of the Kaiser's holocaust poses a profound challenge to the notion that Nazi violence was an aberration in European history. (Faber)

Apparently, the book has been out for a while. This review (click) in the Guardian is dated 2010. Years ago, one would occasionally see references to the cruelty of Germans and other Europeans in Africa, but it was all past history by the time we were born, so nothing was done about it.

-Joe-