Somehow I missed this earlier: The South seceeded over sovereignty issues...
The great "States Rights" shibboleth, one more time. The Thing That Would Not Die.

The antebellum South had no difficulty whatsoever with Federal authority superseding that of the States, as long as it was NORTHERN state laws that were overridden. One example of many: take a good look at the Federal Fugitive Slave Law of 1850; a massive, pro-slavery effort that not only negated northern states' legislation but denied trial by jury and other constitutional guarantees.

slavery had a minor role, but economics had more...
And the entire economy of the South was based upon? (wait for it)...
Negro slavery.

nor was slavery illegal in the North.
If you're implying circa 1798, partly correct. If circa 1840 or later this is simply untrue. Completely bogus.

Guess Lincoln the 'spin doctor' is in good company here on the'Cat, eh?