The blue books
The 1918 Blue Books, commissioned by the British government, provide some of the most clear and detailed accounts of the genocide committed under German colonial rule. The full title of the Namibian "Blue Book" was: "Union of South Africa -- Report On The Natives Of South-West Africa And Their Treatment By Germany".
After World War One, both the British and the South African governments attempted to destroy the records of the account of the genocide. However, a few copies have remained until this day.
The report can be purchased here:
https://www.amazon.com/Words-Cannot-Be-Found-Annotated/dp/9004129812
The 1984 whitaker report
Excerpt from the 1984 Whitaker Report
"The Nazi aberration has unfortunately not been the only case of genocide in the twentieth century. Among other examples which can be cited as qualifying are the German massacre of Hereros in 1904, (12) the Ottoman massacre of Armenians in 1915-1916, (13) the Ukrainian pogrom of Jews in 1919, (14) the Tutsi massacre of Hutu in Burundi in 1965 and 1972, (15) the Paraguayan massacre of Ache Indians prior to 1974, (16) the Khmer Rouge massacre in Kampuchea between 1975 and 1978, (17) and the contemporary Iranian killings of Baha'is. (18) Apartheid is considered separately in paragraphs 43-46 below. A number of other cases may be suggested."