That’s because any other complain was small potatoes. Slavery was the cause belli for the war. Anything else is post war revisionism. You think the ones at the time might have known better than Confederate apologists a century and a half after the fact?
No it wasn't. Maryland had slavery, and so did Delaware, Kentucky, Missouri and West Virginia, and yet no armies invaded them to stamp out slavery.
Trying to force slavery to be the cause of the war is just propaganda meant to justify what the evil powers in Washington DC did to protect the financial interests of Lincoln's backers.
The war had not a D@mn thing to do with slavery, and was all about threats to the money streams of the Northeastern elite, who happened to be the same evil sons of bitches that are still running and controlling Washington DC corruption cartel to this very day.
The Corwin Amendment alone *PROVES* that slavery had nothing to do with why Northern forces invaded the South.
Northern armies invaded to protect the fat cat corruptocrats running Washington DC back in those days. And then they claimed they did it because of slavery.
That’s your opinion.
Slavery wasn’t a big deal in the 1800s. The world had seen every form of slavery and didn’t really think much of it.
But we look back with 21st century eyes and are astounded, oblivious to the fact that much of what happens today, would get your neck at the end of a rope.
States’ rights were a very big deal at one time. Passionately big. Today....not so much in a nanny state.