YOU are not paying attention.
I asked you what the federal government could legally and constitionally do -- in a non-secessionist reality - to end slavery in the southern states, had the political process failed to do so.
Well?
I answered this already very clearly. War. To destroy that government that fails so fully in their duty and purpose to secure the rights of people.
Where does the constitution and/or federal law allow the federal government to go to war with the members of the United States?
There isn't, they were improvising....just like the Confederates. You know, like when the Confederacy suspended habius corpus, before Lincoln did. Or maybe like when the Confederacy instituted universal military conscription, before the Union did. Or maybe like when the Confederates fired on Ft. Sumter, initiating hostilities. They obviously didn't think about that one first, they were just winging it, making it up as they went along.