I should think this should put to rest any notion about what the US Civil War was about.

It was slavery but additionally, it was really about the belief in white supremacy upon which slavery was founded on.

https://en.wikipedia.org/wiki/Cornerstone_Speech

So said this real winner -

Our new government is founded upon exactly the opposite ideas; its foundations are laid, its cornerstone rests, upon the great truth that the negro is not equal to the white man; that slavery, subordination to the superior race, is his natural and normal condition. This, our new government, is the first, in the history of the world, based upon this great physical, philosophical, and moral truth.

So really racism and a lot of falsehoods.