'Manner of Washing for Gold in the Brazilian Mountains', 1814. Negro slaves washing for alluvial gold watched over by a slave master brandishing a whip. Brazil was the largest market in the Americas for African slaves. Between the 17th and 19th centuries 10 million slaves were transported there from Africa. Brazil was the last country in the Americas to officially abolish slavery, which it did in 1888. (Photo by Oxford Science Archive/Print Collector/Getty Images)