I read an old book, THE DEFEAT OF JOHN HAWKINS, many years ago in which slave procurement is told.
Something happening deep inside Africa is sending people fleeing from the interior to the coasts where they have built their own fort to take over the lands of the local native king.
The king prevails on Hawkins to use his big guns to knock holes in the fort and the warriors storm in and take the fortress. A general slaughter of those inside takes place, and Hawkins persuades the king to leave enough alive to take as slaves.
Hawkins sails away with full ships, those alive left behind are then eaten by the conquerors.
He goes to South America and the Spanish will not allow him to sell slaves so he bombards the town, takes it and forces the Spanish to buy the slaves, until he is defeated at Vera Cruz.
The Spanish take possession of all his slaves and ships, except one he escapes in, treat the captured sailors as heretics, burns a few, then sells the captured slaves for their own profit.
Meanwhile in a different book, slaves taken to Mediterranean slave markets are castrated and worked to death in the mines and digging wells.
Maybe the Europeans should have bought their slaves at Mediterranean ports.
Arabs/Muslims took ten times as many black African slaves as Europeans.
And the Arabs/Muslims treated them so badly that there is almost no evidence of this population influx, because most died in a few years and even fewer had surviving children. (Castration of black men to serve as harem guards and servants doesn’t help that demographic maintain itself.)
Conversely, the blacks held by whites have left behind large populations of descendants. They were treated better, on average, by European Christians than Muslims, and the demographics of the world prove that.