At some point the consensus, in certain circles, about the civil war went from "slavery is awesome" to "this had nothing to do with slavery". Where did this idea come from and when?
Although it is a myth with various tenets and authors, probably the most directly responsible is former Confederate General Jubal Early, whose many letters, reviews, and articles in the Southern Historical Society Papers during the 1870s and 1880s promoted the ideas that came together as the "lost cause". Other former Confederates supported the various notions in publications of their own, as well, but Early was probably the most influential.