There's also the climate of the South to consider — until the invention of air-conditioning, factory work in the South would have been at a significant disadvantage. Malaria, too, was an issue within living memory.
People don't realise nowadays how very inhospitable warm climates can be.
And yet millions of people lived and worked there. Agricultural work is backbreaking.
The South didn't even have a shoe factory.
Really, how productive can a workforce be that can't read, that have to be forced to do anything, that will not contribute any improvements, that have to be guarded at all times, that will sabotage the work if they can get away with it, etc.?
How productive would you be if you were a slave?
Slavery is a terrible economic system when compared with free labor. It isn't remotely a surprise that free economies economically bury slave economies.
There's also the climate of the South to consider — until the invention of air-conditioning, factory work in the South would have been at a significant disadvantage. Malaria, too, was an issue within living memory.
People don't realise nowadays how very inhospitable warm climates can be.