> From what I've read about the American civil war is that all historians agree that the rebellion was about the right to hold slaves. The argument about federalisim is a narrative constructed afterwards to evoke sympathy for the rebels.

People often say this but I see no contradiction between the American Civil War being about slavery and it being about states' rights. It was about the states' rights to own slaves!

That aside, the idea that "all historians agree" is absurd.