My guess would have been until the industrial revolution.
“My guess would have been until the industrial revolution.”
The Industrial Revolution was well underway in Europe and Northeastern United States by the time the southern states decided it would be a good idea to succeed from the Union while citing their right to slavery as the primary reason. Apparently, the southerners were a bit slow to get on board with industrialism.
Therefore, even with the Industrial Revolution well underway, the South decided it was easer to succeed from the Union and continue to hold human beings in bondage than it was to accept a changing economy.
The historical Industrial Revolution had been underway for a hundred years prior to the Civil War. If you're talking about industrialization in the cotton industry then that would have lasted another 70 years until the mid-1930's.