There has only been one time in human history where slavery was "racialised". The whole concept of "race" was invented to support this kind of slavery.

The descendants of people who bear the same skin hue of the formerly enslaved still have to live with the stigma caused by slavery.

This (and in many other ways as pointed out by the last commenter), is what makes the effects of the Translantic slavery still reverberate today - because people are still judged by skin colour because of that precedent that was set back then.

I don't know why this has to be continually explained to supposedly intelligent people - wilful ignorance?