If Slavery Hadn't Ended
There is, however, a disturbing possibility in the other direction, which I do not think anyone in the thread has mentioned. The literature on slavery suggests that how successful it was depended in part on the cost of monitoring slaves to make sure they were working hard at what the owner wanted them to work at. Some forms of agriculture, notably cotton and sugar production, could be done by gang labor—a lot of workers working together, all doing the same thing—making it relatively easy to identify and punish workers not doing their job. Other forms involved a lot more individual labor and individual decisions, making it harder for one supervisor to adequately control a lot of slave workers. In the latter forms, such as growing wheat, slavery was roughly competitive with free labor, meaning that if slaves were cheap and wages high it paid to use slaves, if slaves were relatively expensive and wages low it paid to hire free workers instead. In forms of agriculture suitable for gang labor, on the other hand, if slavery was an option, as it was in the southern states and the West Indies, free labor couldn't compete. The advantage—from the standpoint of the slave owner—of being able to work slaves harder than free workers without having to pay for the resulting disutility to the workers outweighed the disadvantages of using slaves.
Assembly line labor for industrial production, of which the famous early example is Ford motors (there were, of course, precursors), looks a lot like gang labor agriculture—a form of production in which it is easy to see whether or not each worker is doing his job. Ford's version was developed about fifty years after the Civil War ended slavery in the U.S. That suggests the possibility that if secession had been successful and slavery continued, the Confederacy might have ended up as a successful industrial society, with gang labor agriculture gradually replaced by assembly line production–still using slaves.