I'm sure nobody cares what I think, but I believe, that except for some New Englanders and Kansans, the majority of Northerners fought the war to fulfill a duty to their country and to restore the Union. I believe Southerners fought they war because they felt they had the right to secede and defend their new country. I do not believe the North would have needed to restore the Union nor the Confederacy need to defend a new country without the institution of slavery. I believe secession was the cause of the war and slavery was the cause of secession. I can't imagine any other issue that would have caused eleven and by some counts thirteen states to leave the Union as a group. Without such a large group of states, a new country would not have been viable or defendable.
But, that's just my opinion.
Jim