If I recall properly, the US accounted for about 3% of the total slave trade.
At worst we are on the hook for 3% of the total.
On the other hand, showing a limited slave trade from Africa to the Muslim countries is a crock. They were/are pushing slavery from 650AD to today. The South African army forced Ethiopia (Abyssinia) to outlaw slavery after WWII. Saudi Arabia did not outlaw slavery until 1962 (under pressure from the West). Muslim Northern Sudan enslaves Christians and animists from the South today.
The slave lines to the Muslim world, on that map, should be much thicker and pronounced. The reason there aren't that many black skinned people in those Arab countries is because they castrated the males, and killed the babies of the concubines.
Peter Hammond had some good talks on this subject.
If I recall properly, the US accounted for about 3% of the total slave trade.
It is ironic and interesting that the places where the most slaves ended up are now desperately poor nations and the blacks who live in the US are much better off because their ancestors were sent here as opposed to the Caribbean or Brazil.