I've never lived south of the Mason-Dixon line, and I was taught while growing up that the civil war was about slavery. But that's not quite right: the civil war (or, if you prefer, the war between the states) was about states' rights (as guaranteed under the constitution at that time), with slavery being the catalyzing factor. In order for the tension to erupt into war there had to be an issue that was sufficiently repugnant to one side and essential to the other, and slavery was that issue.