I guess my point is that industrialization doesn't/didn't occur uniformly across entire industries; some aspects of industries were mechanized before others, temporarily increasing demand for manual labor in the per-industrialized segments to keep up with the machines. Textile factories create demand for field workers, steel mills and steam engines create demand for coal miners, railways create demand for workers that lay rail, etc.
Another example, in an alternate timeline perhaps, might have been the development of the western territories. Instead of Chinese immigrants building most of the rail, it probably could have been a very profitable venture for slave owners. Slave labor was used for railway construction in the south, so it's not far-fetched.
I agree that slavery was destined to lose in the end, but I don't think industrialization is a direct path to the economic obsolescence of slavery, because slave labor can compliment partial industrialization.
I seriously doubt slaves would have been profitable for the western railway. Blasting tunnels was very skilled work, and very dangerous. Would you want slaves, who hated your guts, handling nitroglycerin? You'd need as many armed guards as slaves.
Presumably the blasting itself could have been done by specialist free men. But the blasting itself is only a small part of the process. First you need to drill the holes by hand, that means beating a rock drill with a hammer for hours, just for a single hole, and you need dozens of holes for one blast, countless thousands if you're trying to go through a mountain.
There were steam powered machines for drilling rock at this time, but they were cumbersome and temperamental, most of the drilling was still done by hand. Hence the folklore of John Henry racing a power drill to see who could work faster. I believe most of the drilling in the west was done by hand, by Chinese immigrants.
Then there is the matter of the rubble. Explosives only break the rock, who hauls that broken rock? That's more manual labor.
The nitroglycerin would be of necessity readily available. Do you really want your slaves around this stuff? Think they might steal a bit and put it in the overseer's tent at night? You'd have to spend more money on armed guards and manacles than just hiring free men. Slaves were also costly to buy.
Another example, in an alternate timeline perhaps, might have been the development of the western territories. Instead of Chinese immigrants building most of the rail, it probably could have been a very profitable venture for slave owners. Slave labor was used for railway construction in the south, so it's not far-fetched.
I agree that slavery was destined to lose in the end, but I don't think industrialization is a direct path to the economic obsolescence of slavery, because slave labor can compliment partial industrialization.