That was part of the 1877 Compromise. In return for the restoration of white democracy, the South agreed to sit on the black population. They were able to move north in only small numbers because the jobs they could handle were being filled by European immigants. The Cotton industry continue to dominate the Southern economy, but the old land-owning class had been broken by the war. The lost their slaves, but equally bad, they had lost their accumulated wealth and their best and brightest had been killed or maimed in the war. The English had found new markets elsewhere, and so the return on cotton was never again as great. No second act for the Southerns who had created and dominated the ante-bellum USA.
Until the 1947 Taft-Hartley Act allowed states to pass "right-to-work" laws, making Southern states increasingly attractive for business.