WIJG: None of which refers to the formal withdrawal of a State from the union, under the Constitution as it existed in 1860."
Key point: the US Civil War was not caused by secession alone. Indeed, had there been no violence by the South against Federal facilities, ships and people, there may well have never been war.
Certainly President Buchanan was determined to avoid violence, and did so, even while he attempted to support Federal forces at Forts Pickens, Taylor, Jefferson and Sumter.
President Lincoln continued Buchanan's policies, while announcing publicly that "The government will not assail you. You can have no conflict without being yourselves the aggressors".
President Jefferson obliged Lincoln by destroying Fort Sumter and forcing its surrender. Lincoln declared that an "insurrection" and Jefferson then declared war on the United States.
So it was not secession which caused the war, it was Southern insurrection and rebellion.
Once again, I'll state my opinion of secession. Secession, if peaceful, lawful, negotiated and approved by Congress is one thing. Violent insurrection, rebellion, "domestic violence" or invasion of the United States is something else entirely.
Another irrational statement - if secession was constitutional, then the resulting hostilities were NOT "insurrection and rebellion." And you have failed to prove State secession circa 1860-1861 unconstitutional.
In fact, given that the Constitution nowhere prohibited State secession, the maintenance of federal forces within Fort Sumter following the withdrawal of South Carolina from the union, was an act of war on the part of the remaining United States...