George Washington Williams 
History of the Negro Race in America from 1619 to 1880. Vol. 2 : Negroes as Slaves, as Soldiers, and as Citizens [EPUB ebook] 

George Washington Williams was an American Civil War veteran, minister, politician, lawyer, journalist, and groundbreaking historian of African-American history. Shortly before his death he travelled to King Leopold II’s Congo Free State. Shortly before his death he travelled to King Leopold II’s Congo Free State. Shocked by what he saw, he wrote an open letter to Leopold about the suffering of the region’s inhabitants at the hands of Leopold’s agents, which spurred the first public outcry against the regime running the Congo under which millions lost their lives.