The black demographic moved from Republican (freeing the slaves, right to vote, etc.) to Democrat during the Great Depression, when FDR started promising freebies.
I suppose it could go back that far...but I was thinking along the lines of "The War On Poverty" which that filthy racist LBJ "declared" in 1964 (I looked it up after my post).
LBJ is reported to have once commented,regarding the "War On Poverty" something like "I'll have those ******* voting democrat for the next 200 years."
I don't have the first clue if he ever said that but it's easy to see how the leaders of Rat Party at that time *believed* it.