As long as we're guessing my guess is that slavery would have ended in the South in the near future (5 or 10 years is as good as any guess) without the CW, not because of farm machinery but just because world opinion was rapidly changing on the matter. (Brazil was the last to free its slaves in this hemisphere, in 1890, and it had a huge slave population). Many of the Confederate leaders knew this and welcomed it (including Lee and Davis).
The Founding Fathers expected slavery to die out in a generation in this country. That's why they didn't deal with the problem. It was the cotton gin and the spinning jenny which made cotton so valuable and it was very labor intensive to plant and pick.
England deserves most of the credit for the anti-slavery movement (Wilberforce, et al,) but the US was not far behind. Until this movement gained force slavery had the approval of religion and law. There had always been slavery. It was an accepted social phenomenon. That changed during the mid-19th Century.
in point of fact, my people had kept slaves in this country for at least 10,000 YEARS (perhaps 25-30,000 years MAY be closer to the REAL number.), so the American Indian culture certainly accepted the "peculiar institution".
as for the clout of the anti-slavery movement in the 1800-1860 period in the USA, a former chair of history at Tuskeegee University said (during a seminar i attended in grad school daze)that, "there was in 1860, not 10,000 people in the whole country who cared a damn about the plight of the slaves. they should have;they did not."
free dixie,sw