If it was about slavery, why didnt the North start in their own backyard. Lincolns family through marriage owned slaves. Northern Generals Sherman and Grant also owned slaves. The Emancipation Proclamation only freed slaves of the Confederacy. Northern Slaves remained slaves until after the war.
Very few Southerners owned slaves, less than 3% and they were mostly the rich not the ones fighting.
The South was fighting because their land was invaded by an Army.
The North was fighting for, well you tell me.