Just to be clear, slavery is 100% legal in the United States if it is punishment for a crime. Read the 13th amendment. Many people already see the prison system as an abhorrent extension of slavery. Legally speaking, it literally is.
Also, Christopher Columbus was tried in Spain and imprisoned for his atrocities in America. There was never a point in time where slavery was unanimously accepted. Institutional racism was born because enslavement between two equal humans is so clearly wrong. Slavery was so clearly a big deal that one party needed to be dehumanized to justify it.
Capitalists make portable suicide booths called guns! They love them