Over at Strange Maps appears this intriguing map, apparently drawn up in spring or summer of 1861:
In this map, West Virginia (still tentatively naming itself for the Kanawha River) and Maryland have slice apart most of Virginia, leaving the Old Dominion a landlocked sliver of its former self. After the war, no rearranging of state boundaries occurred, but WV did secede from Virginia and gain admittance as the 35th state in 1863. Both the proposed partition and the actual emergence of WV are highly unconstitutional, as Article IV, Section 3 reads in part:
"[N]o new State shall be formed or erected within the Jurisdiction of any other State; nor any State be formed by the Junction of two or more States, or parts of States, without the Consent of the Legislatures of the States concerned as well as of the Congress."
That's pretty plain for a legal document: none of this could be done without the consent of the Virginia legislature, which of course was never offered. If truth is the first casualty of war, law often falls bleeding beside it.
Now, you could argue that Virginia was no longer protected by the Constitution, having seceded, and so the westerners had every right to secede from the country in the same way that the American revolutionaries had seceded from England. But that would make the Civil War an act of aggression against another country and the North never accepted that characterization; the whole premise of the war, from the Union perspective, is that the Southern states were still part of the United States all along and those federal armies were just putting down and insurrection. So the Constitution ought to still apply.
The Southerners found that argument more attractive in 1866 than they had in 1861 and were happy to argue that they were still in the Union, exactly as before. By now, though, the Republicans had also changed their minds. The Southern states were outside the Union, after all, and wouldn't be allowed back in until they had "consented" to a few alterations to that Constitution ....