It wouldn’t do any good to say that there were slave states in the Union, or that the war was about preserving the Union, not slavery.
I always felt that states rights was the camels back and slavery and the right of a state to leave the Union was the straw that broke it. Lincoln intended to preserve the Union. Doing so had to abolish slavery as part of that effort. IMO
I think that's more right than wrong, but those two do not separate neatly.
One-eighth of the whole population were colored slaves, not distributed generally over the Union, but localized in the southern part of it. These slaves constituted a peculiar and powerful interest. All knew that this interest was somehow the cause of the war.
Why inject historical facts and reality into the conversation? What's wrong with you?