I agree plenty of history happened in between, but your notion that they're unrelated is absurd. Nobody today learned English from Alexander Hamilton, but nonetheless we not only understand the Federalist Papers just fine, we live by many of the ideas he expressed. Culture is handed down.

If you'd like to better understand that, I'd suggest you read Kendi's "Stamped from the Beginning", who gives an intellectual history of America's racist ideas. I also think you're mistaken to lay the current troubles at the feet of formal segregation policies, which were only active in one part on the US. Maybe go read "Sundown Towns", which shows that all across America we had towns with de-facto segregation without formal policies. And it takes only a glance at modern maps showing race to see we haven't solved the problem.