Since you know we are talking about Civil War monuments why are you dragging the Lincoln Memorial (1914-1922), the Jefferson Memorial (1939 - 1943), and the Washington Monument (1848 - 1884) into the discussion?
I am sure it was just coincidence that the Civil War memorials in question didn’t start cropping up until the Jim Crow days.
Some, such as the Robert E Lee Monument in St. Louis were erected rather quickly. The Robert E Lee Monument was finished in 1884. It was to commemorate the person and general that Robert E Lee was, and had nothing to do with slavery.
Of course those kind of things can be found out by digging through historical records.
Yes, “Some”, that was almost 20 years after the war and St. Louis was not crushed during the war like much of the south.
They also had a huge economic boost when the post war land rushes in the west began as it was a major transportation hub and jumping off point for many of the wagon trains. It was also a major Mississippi port and rail hub.