The Herero and Nama ethnic groups in Namibia had rebelled against German rule in response to the expropriation of their land and cattle by Germany.
The head of the military administration in the region, Lothar von Trotha, ordered the massacre in response to the uprising.
The indigenous Herero and Nama people had to flee their lands. Those killed were people found trying to return to their expropriated lands.
About 65,000 of the 80,000 Herero and 10,000 of an estimated 20,000 Nama people are thought to have died.
According to many published reports, victims were subjected to harsh conditions in concentration camps, and some had their skulls sent to Germany for scientific experiments.