If allowed to secede, the people of the South would have gone through paroxysms. Circumstances were such that they had become utterly dependent upon a way of life that was immoral, even depraved. Rebellions against it were inevitable (by both slaves and enlightened whites, probably of the next generation). But at least the struggles would have been internal. Conquest by the North made white Southerners more unified and recalcitrant for decades and decades.