H.H. Johnston, A History of the Colonization of Africa by Alien Races, 1899.
John A. Hobson, Imperialism, A Study, 1902.
E.D. Morel, Red Rubber: The story of the Rubber Slave Trade which flourished on the Congo for twenty years, 1890-1910. new and revised edition 1920.
Adam Hochschild, King Leopold’s Ghost: A Story of Greed, Terror and Heroism in Colonial Africa, 1998.