More can always be written, but you may find these excellent answers from u/freedmenspatrol and u/400-Rabbits to be of assistance:
https://www.reddit.com/r/AskHistorians/comments/6ygc7p/comment/dmnx8re/
https://www.reddit.com/r/AskHistorians/comments/1etwsk/why_was_international_slave_trading_banned_both/