The Civil War was a conquest of one region by another region.
Re: slavery . . .
It was on its way out. It was disappearing from one country after another during the eighteenth and nineteenth centuries. Yes, the American South was relatively recalcitrant, but I highly doubt they would have been able to buck the trend for many more decades. Ideally a younger generation of Southerners would have said “this is just not viable anymore” and found a way to phase it out. That would have been much, much better than having emancipation imposed during a war of conquest. The latter scenario made the South so embittered that African Americans then had to endure a century of the horror of Jim Crow.
Conquest always embitters. That’s why World War I segued into World War II — due to German embitterment.
The Civil War was PRIMARILY about the Northern industrialists being upset that an independent South would send its cotton to Great Britain instead of to the textile manufacturers of the North. The South was conquered for that reason.
The South had been a contiguous region developing a different culture from the North. The South should have been allowed to secede. I believe it would have been better for all involved EXCEPT THE NORTHERN INDUSTRIALISTS. Screw ’em.
We’ll never know, but I think the acceptance of secession would have been: [a] better for Southern whites; [b] better in the medium term for Southern Blacks; [c] better for the Northern masses. The elites always use the masses as cannon fodder, and that certainly pertained to the Civil War. We hear so little about the draft resisters of 1861 and 1862.
By the way, Karl Marx (prone toward centralism and industrialism) was totally wrong to cheerlead Lincoln and the Northern cause.