You might find this thread very illuminating, in what I think is one of the most informative posts I've ever read, by none other than /u/sunagainstgold.

The last paragraph is a pretty good conclusion, but the whole post is great.

All these strands--the idea of legal discrimination based on ancestry; the idea of ancestry-based "biological" inferiority of black people to white people; the idea of slavery--came together in 17th century British North America. It's readily apparent that free black people and free white people, indentured black servants and indentured white servants coexisted in the early years of colonial Virginia. But the designation of specifically black people as slaves not only institutionalized pre-existing ideas of prejudice, but magnified and propagated them with disastrous future consequences.