 By the 18th century, Angola had become one of the principal sources of the Atlantic slave trade.Following the British and United States' bans on the African slave trade in 1808, it declined, but the period after still accounted for 28.5% of the total volume of the Atlantic slave trade.Between 1810 and 1860, over 3.5 million slaves were transported, with 850,000 in the 1820s.