I've wanted to write on Ed Baptist's new book The Half Has Never Been Told for a while. I haven't had the time and I probably won't, which is why I want to point you to this review from The Junto which covers the themes and the major ideas. In particular, they get at one of the most important ideas in the book; that at the time of the Civil War, slavery wasn't dying:
Specifically, Baptist argues that antebellum slavery worked. It was a highly (and increasingly) efficient labor system. As the source of America’s most important commodity, it stood at the center of American capitalism, both southern and northern. And as the central fact of American capitalism, it drove U.S. expansion into and beyond the Mississippi Valley.
Again and again, Baptist draws the reader’s attention to the figures for yearly southern cotton production. His crucial claim, spelled out in chapter four, is that increases in cotton productivity before the Civil War resulted not primarily from improved machinery or breeds of cotton, but rather from the refinement of the “pushing system” on southern plantations. Overseers, applying the logic of commodity capitalism to the labor of field hands, learned how to set escalating daily picking quotas, enforced by brutal punishment, for maximum efficiency. Baptist calls this labor system “the whipping machine,” after a torture device supposedly invented by one entrepreneurial Louisiana planter to extract labor from his slaves. Considering the place American cotton had in world manufacturing, Baptist argues, this means that “systematized torture was [crucial] to the industrial revolution”—and thus to capitalism itself.
There's no reason to think that these productivity gains would have slowed, or that Southern planters wouldn't have found new ways to use slave labor and integrate it into a modern economy. And there's no reason to think they wouldn't have support either. Slavery was so integral to the American economy—so key to global finance and manufacturing—that enslavers would had plenty of allies had the institution continued. (There's a reason the Confederacy worked hard to get recognition from Britain and France during the war.)
American slavery didn't end because the practice—which formed the bedrock of Southern society—was dying out. It ended because slaveholders overreached. They reached for too much power, and when they finally found a foe in the Republican Party, they left the nation and started a war which—after a few years—they couldn't win.
To borrow from historian Mark Noll, don't thank some moral awakening for the death of that peculiar institution, thank the Reverends Ulysses S. Grant and William Tecumseh Sherman.