James McPherson’s Battlecry of Freedom is widely considered to be the best single-volume history of the Civil War, and devotes considerable attention to exactly these questions. I cannot recommend that volume enough to someone interested in these topics.

Suffice to say, the North was considerably more industrialized by virtually every measure than the South by 1861. After the rail-building boom of the 1850’s, the US had the majority of the miles of rail track on Earth. The vast majority (over 2/3rds) of this track was located in the North, the steel had largely been manufactured in northern foundries made from ore from northern mines, and with lumber milled in the North from northern forests. These rail links, combined with the North’s superior water and canal network, allowed lower transportation costs that created a practical market for mass-produced consumer goods, whereas 40 years earlier most clothing and tools would be made within a few miles of the consumer. These new markets encouraged specialization and the investment of capital that transformed the nature of labor demand in many industries. This produced an economy increasingly built on wage-earning rather than individuals directly producing goods for market. This was much more productive, but also lead to a profound change in the relationship between a worker and the market.

This transformation was very new, and frightened many people in America just as it had when England experienced its own industrial transformation thirty years before. Now there were managers, factory owners, and “bosses” in between the worker and the proceeds from the sale of their production. As the popular press of the South became more and more resentful of criticism of slavery by northerners, a popular issue for southern authors to fixate on was this strange new labor relationship arising in the North. At the time, it was pointed to as the cause of terrible poverty in northern tenements, the plight of wretched immigrants, and “proof” that the North enjoyed no moral superiority over southern slave owners.

This argument was not that strong at the time, as Americans in the North enjoyed one of the highest standards of living in the world. By some measures, the South was “wealthier” per capita than the North, but that was only due to the huge asset-value of the South’s slaves. And one of the clearest and most dramatic differences between the northern and southern populations was literacy. The North has aggressively embraced public education and was a world leader in the availability of education. Adult literacy in the North was near 95% (nearly the highest in the world) with 3/4ths of children enrolled in school for an average of six months a year, while in the South white literacy was nearer 80% with one third of children enrolled an average of three months a year. So it is difficult to argue that the Northern people suffered terribly from their choice to go without slavery.

And finally, in the modern context we have largely answered the question of the “justice” of wage labor. The arrangement no longer seems so alien, and after a great deal of argument, reform, mitigation, and struggle, it has become rare for a person to view it as inherently wrong. One thing is for certain: few people are clamoring to go back to making their own shoes by hand.

Edit: one caveat I should add is that the North was more industrialized than the South, but I mean this only in relative terms. In 1860, 80% of the population of the United States did not live in cities. The modal northerner was a farmer, by a wide margin.