I recall a show, and I’m pretty sure it was animated (Simpsons, I think), where a woman (Lisa?) is being interviewed for a job/position, and asking about the cause of the USCW.
She starts going into federalism/antifederalism, the political climate of the time, and it’s beginning to be a long answer.
The interviewer tells her “just say “slavery.””
And she looks downcast and mumbles “slavery…”
Now that I think about it, I’m pretty sure the episode is where she writes and essay and goes to Capital City.
From what I’ve read, slavery was an issue, not the only one, but a core one. Also, the Emancipation Proclamation was more a means to shut down the South’s fighting capability than a humanitarian effort. It also had no affect on border states and Union states.