I will definitely give the WWI a listen. I went and saw the They Shall Not Grow Old film and it was amazing. Those guys were another level of tough.
The South was clearly desperately grabbing hold of a dying method to a changing economy. Along with the morality dilemma (that wasn't going away), Slavery would have died eventually with soon to be invented mechanic systems, that drastically reduced the labor requirements of farming. No way to know for sure, but my guess is it would have dissipated naturally by the 1880-1890s. In 1830, it took 3 labor hours per 1 bushel of grain. By 1890, that had changed to 1 labor hour per 2 bushels of grain. That is a 600% increase in labor efficiency. Cotton however was still more labor intensive, until the cotton picker was invented (1940's), so who knows. Glad we are 150+ years removed from that now.