Kidnapping people and selling them into slavery, as was done to Africans and others throughout history, is forbidden by the Eighth Commandment. That is one reason no one with even an elementary understanding of the Eighth Commandment could ever use the Bible to justify the most common manner by which people became enslaved: kidnapping.
The early rabbinic tradition interpreted this commandment as specifically referring to kidnapping. This commandment was always understood to mean, before anything, we are not allowed to steal human beings.
