David Frum wrote a nice piece about this topic in the context of commemorating the 25th anniversary of Battle Cry of Freedom. His salient points:
From time to time, we hear denials of the centrality of slavery to the Civil War. That’s apologetics, not history. Slavery was always, always there: the war’s fundamental cause, the war’s shaping reality. [...]
Whether American civilization was to treat some men as property – whether in fact the right to treat men as property was indispensable to American freedom – that was the question for which Americans fought and died a century and a half ago.
I’m contemplating a book that utterly turns over the notion of the Confederacy as this noble, gallant Lost Cause and re-casts all of the appropriate players, Lee, Davis, Jackson, and all of their apologists, as treasonous, sadistic, sociopathic villains who disguised the inherent cruelty of the South under the almost translucent banner of states’ rights and liberty, and, in the name of preserving their terrible “institution” of slavery, were responsible for 650,000-plus dead Americans. Pull no punches.