They not only owned them, almost all of the actual slavers who captured them were either Black or Arab...who then sold most of them to middlemen, who were primarily from countries speaking English, Spanish, or Portuguese.
This pisses me off, about how the history of slavery's portrayed.
I'm not excusing anybody who ever indulged in slaving, but Africans seem to be overlooked when it comes to the blame game.
Most, if not nearly all, slaves brought to the western hemisphere came from western Africa.
The Portuguese and the English had forts on
the coast of western Africa; they didn't dare venture any further inside that continent until the late 1800s, decades after slavery had been abolished.
There was a reason; those of European derivation couldn't handle the climate or the terrain.
That's why, incidentally, in the British colonial empire, its colonies in western Africa were among the first granted independence; they wanted rid of them, as they'd never been able to establish themselves, as they had in southern Africa and eastern Africa.
During the slave-trading era, it was
Africans who brought other Africans from the interior to those coastal ports, and sold them to slaver-buyers.