I don’t think the civil war was completely nonmaterial. The slaveholding south was genuinely scared of even the moderate abolitionism espoused by Lincoln who wanted western states to be free states. This would tip the scales in congress in favor of free states in time, allowing for the abolition of slavery by law. The slaveholding south saw their power eroding, which is why every compromise for new states was extremely contentious and why Kansas ended up in civil war in the lead up to the real civil war. So I don’t know how correct it is to say the south left for no reason, since Lincoln really did represent a threat to their interests (albeit an extremely moderate one)