Back in the late 1960’s, Michigan’s history text books stated that the war started over tariffs, taxes and because the Southern States were getting too cozy with England on their own. I don’t think The Lost Cause had anything to do with it, but I don’t know for sure.
It did, at least indirectly. Keeping the country together meant not antagonizing the South. The Democratic Party of Wilson and FDR relied on Southern votes, and progressive historians didn't like big business, industrial capitalism or the Republicans, so the tendency was to downplay slavery and accept much of the Southern view of the war.