How can a state that has seceded from the Union be bound by a Constitution that is an artifact of that Union? You’ll recall that the Confederacy established its own Constitution, leading to the inescapable conclusion that it no longer considered itself bound by the Constitution of the United States.
You’re simply restating the crux of the argument. The Constitution does not grant any rights, including the right to secede. But the Enumerated Powers clause of Article I, Section 8, and the Tenth Amendment allow that, absent any explicit delegation of that authority to the Federal Government, it resides in the states. Since the Constitution does not expressly forbid secession nor does it delegate that power to the Federal Government, it is a power reserved to the states (or the People).
Your whole defense turns on the notion that states are not allowed to exercise sovereignty. If they are, your argument crumbles. Yet you cannot refute my contention that the Confederate secession was perfectly legitimate, except by invoking a circulus in probando fallacy: the Confederacy could not secede because it was part of the United States, and it was inviolably part of the United States because it could not secede.
The 10th Amendment doesnt apply here because the constitution defined the mechanism for admission and consent authority for the construction and definition of the states to the Congress in Article IV, Section 3, Clause 1.
Had he not, SC could have dissolved its legislature, called new elections and created itself a new entity, just as the United States of America did. The new entity, no longer being South Carolina, could have made compensation to the United States for property seized under the new government, and then, had the Yankees not agreed, have had a valid claim to "invasion."
That did not happen because South Carolina unilaterally voided its ratification of the Constitution without first seeking legal redress, and stole property from the United States.
In any event, the question of who started the war is clear: the traitors started it.