Taxation was the original issue. Slavery was used to sway public opinion against the confederate side of the original taxation conflict. And Lincoln knew that. I mean, after all, who would support a side that had slavery right?? So it has become the war against slavery in modern fairy tale history. I know it's hindsight but if the south had abolished slavery on their own, the north would have lost that trump card and had no real good reason to do what they did from a PR perspective.
Well not to flog a horse, that if not dead is at this point in mortal danger of expiring, but a couple of points....
If you will look at the confederate constitution you will see that they had already abolished the slave trade, which means slavery was on it's way out. Add in the advances in technology and it is a no brainer. Slavery did not become an issue until the second year of the war.
Revisionists history runs rampant.