Paul Hockenos reviews Jeremy Sarkin's Germany's Genocide of the Herero: Kaiser Wilhelm II, His General, His Settlers, His Soldiers and David Olusoga and Casper W. Erichsen's The Kaiser's Holocaust: Germany's Forgotten Genocide and the Colonial Roots of Nazism.
If you don't have time for book-length treatments of this topic, then you might consider looking at chapter 33 of Thomas Pakenham's The Scramble for Africa: The White Man's Conquest of the Dark Continent from 1876 to 1912. Judging, though, from the audio excerpts read by Mr. Olusoga, you'll find much more about German racial attitudes in these new works.