Blacks were not, needless to say, part of the phrase "all men are created equal".
This powerful myth existed long after slavery ended and had embedded itself like a foul odor into accepted belief to such an extent that it persists to this day.
The cyclical effect was such that even after abolishment of slavery blacks lived under much poorer conditions which only reinforced the stereotype that they were less intelligent and less able to prosper.
It once again confirms that we should never underestimate the capacity for some human beings to be complete dimwits at well as vile pieces of shit to each other. My adopted country was only marginally better.
I am not sure we are any smarter today.