Political power was the key. The South was not concerned with slavery being abolished, especially since the north was offering an amendment to the Constitution to guarantee it’s continuance where it CURRENTLY existed. This was the rub. Current existence would mean that all new states would be in alignment with non-slave holder states interest.
Political power IN PURSUIT OF SLAVERY. Apart from that, the South had excessive political power for its free population.
And political power to keep & expand slavery meant the war WAS about slavery.