The best way to put it, I think, is that slavery was a necessary, but not sole, cause of the Civil War.
I guess so, but what about the Compromise of 1820, 1850, including the Fugitive Slave Act, the unsuccessful, but very controversial Wilmot Proviso, the Kansas-Nebraska Act, The Dred Scott Decision, et al. I simply cannot imagine anything else as compelling for war than the issue of slavery. Tariffs, sectional dislike for one another, sure. But without the issue of slavery, civil war might well have been averted.
It's fun to speculate, though.
Thanks for your note!
The South claimed that 'States Rights' was their reason for seceding. Well, the 'State Right' foremost in their mind was the preservation and extension of Slavery into the new territories. It's all semantics, folks.