Slavery had nothing to do with it. That is a 4th grade articulation of the conflict. New England almost secceded before 1805. The north and south was always a power struggle
Discussion
Read the statements the states made who seceded. The south seceded because they feared slavery was going to be outlawed. Sure there were other issues, but that issue came up over and over in their statements.
The North didn't fight to free the slaves. Lincoln didn't use it as a means to an end. The North had slaves during the war. It wasn't even the North's concern at all. But it was the South's fear.
You are wrong about a 4th grade view. The 4th grade view is that the North fought to free the slaves.