Red Rubber: The Story of the Rubber Slave Trade Flourishing on the Congo on the Year of Grace 1906 | E D Morel
A documented and highly charged contemporary indictment of the Belgian exploitation of Africa during the height of the imperialistic age, first published in 1906 with the support of British antislavery organizations. This expose, by a horrified British investigator, of the atrocities committed against the natives of the Congo by soldiers in the employ of King Leopold of Belgium has an introduction by Sir Harry H. Johnston. This title is cited and recommended by The American Historical Association's Guide to Historical Literature.
Red Rubber: The Story of the Rubber Slave Trade Flourishing on the Congo on the Year of Grace 1906 | 
