@Arthur_500 To say "not slavery" you have to ignore the ignore the facts and the history and the documents and the speeches.
Of course there are details to it, there always are, the particular paths people took to get to where they eventually arrived, but there is no other issue more central, no other issue that pops up everywhere, than slavery.
The Constitution and the Union with their compromises were built on a crime against humanity, and finally enough people couldn't look away, and enough people were dependent on that crime and couldn't give it up, that something had to give.