The South's leaders, speechifiers, Pulpit pounders, newspapers, and Secession Commissioners didn't preach leaving the union because of taxes, tariffs, sectionalism, or whatever other reasons the modern day Southern Heritagist's are preaching now...

They used the fear that Slavery (as the South liked having it) was going to be taken away from them. Slavery was the fulcrum they used to leverage fear that death, ruin, mayhem that would follow the Republican’s freeing the slaves, and equalizing them with White Southernors.

“We appeal to the Women of the land. If we would keep our fair South free from the curse of Negro equality; would keep forever the slave in the kitchen and cabin, and out of the parlor; would wish a national Capitol, where they will not be elbowed by Negros in the gallery of it’s Senate…if they (the mothers of the States) have sons who can vote…vote for secession."
(Augusta Daily Constitutionalist January 1, 1861)

The South left the Union because of the slavery issue. The North went to war to bring the south back in. I'd say the war was about slavery

Kevin Dally