No American ever captured human beings to force them to live in slavery.
Slaves in Africa were capured by black Africans, usually members of a rival tribe. They were bought mostly by other blacks or Arabs. Some were bought by Dutch or Portugese slave traders and taken to America.
Americans who bought slaves were not blameless, but hardly the only ones at fault nor the worst. The worst were the black Africans who captured them in the first place. The ones who made it out of Africa were actually the lucky ones. The slave traders' descendants are now living in cardboard boxes on the mean streets of Nairobi, while the descendants of slaves are living free in America.