http://www.liverpoolmuseums.org.uk/ism/slavery/africa/capture_sale.aspx
https://www.amren.com/news/2013/03/did-black-people-own-slaves/
https://www.accessgenealogy.com/native/indian-slavery-and-slaves.htm
Also, ever here of abolitionist?  And who do you thing voted to allow to let women and blacks to vote?