OTOH, the Union did not abolish slavery until well after the war, and several slave states stayed in the Union.
You also missed the fact that most of the Confederate soldiers were draftees.
While the people who engineered the secession were concerned with slavery and its extension, Lincoln and the Republicans were not going to abolish slavery itself.
The North was fighting to preserve the Union, not to end slavery. The Emancipation Proclamation freed the slaves in states that the Union didn’t control. It was directed at harming Southern morale and possibly igniting a slave revolt.