The reason the South never industrialized was the Slaver aristocracy had the region under their iron fist and did not want it for various reasons particularly the loss of power to a rising bourgeois class which industrialization would produce.
And that cost the South, and they got their’s handed to them by the North.
Karl Marx wrote a lot of that stuff for the New York Daily Tribune when he was closely following the American Civil War. But he never set foot in America and was full of his Class Warfare nonsense so he believed it. Bizarre to see it still echoing today.