Comment by inglor_cz

"What we'd now call the developed world."

The developed world of now is much more extensive than the developed world of the 1860s, and the South was very backward until the 1950s or so. In the 1850s, it was seriously lagging behind the North in industrial power, which is one of the reasons why they lost the war. This would point to a yet another chicken-and-egg problem. Nonfree labour tends to cement premodern societal and economic structures, which perpetuate existence of non-free labour, unless disrupted from the outside. The Islamic world didn't give up slavery voluntarily either.

I am not sure if we can call the South of the 1860s "developed", even relatively to the rest of the Western civ. By what criteria?

"The Russians you mention managed it in 1723"

Serfdom in Russia was abolished after the Crimean War, and the Tsar used the money gained by the Alaska Purchase to pay off part of the due compensations to the nobles.

Yes, these institutions were not equal. Different cultural and historical development. Still, a Russian serf of the 1850s was a very non-free person, tied to the land and dependent on whims of his lord or lady. Few would care if a drunk noble whipped him to death, even though theoretically he should not be doing that. A rough equivalent in category.