The evidence that the Civil War hinged on the question of slavery is indisputable. Even contemporaries on both sides said it. It was only later did apologists (yes, including the KKK) whitewashed the question with the broad states rights propaganda.
The South wanted to preserve (and expand) slavery and said they had a right to protect the institution by ceceding from the union. That was the overarching reason, all other factors were fairly insignificant and would not have led to treason, ah, war. Yes, at first, the Union would have traded slavery to bring back South, but that was not going to happen because the South didn't trust the Union on slavery and the abolishinists were growing strong each year.