Actually, if you include the trans-Sahara slave trade, many more Africans perished in that than in the trans-Atlantic slave trade. And that trade might still be going on under the law's radar.

Read John Azumah Adembillah's The Legacy of Arab Islam in Africa. Many more than 6 million were trafficked to the Middle East over fourteen centuries and SIX TIMES their number died in the desert. And it was British soldiers who prevented Arab traders from Zanzibar from denuding what is now Tanzania and Zambia in the same way.