That was an insurrection which the federal government is EXPLICITLY empowered to repress insurrections in the Constitution. See Article 1, Section 10, paragraph 3 and tell me what that says
No state shall keep troops or ships or enter into external compacts?
I think you mean Section 8, paragraph a bunch, about calling forth the militia to prevent insurrection? The issue here is that it’s not an insurrection - that’s when a small group is rebelling against the legitimate authority. What actually happened was that that same legitimate authority (the state) no longer recognized a higher authority (FedGov) it ceded some powers to. It simply revoked giving those powers to the US, and instead reclaimed them for the state / ceded them then to the Confederacy.
But deliberately lying about the meaning of words has long been a liberal tactic.