Replies

Then why did the US specifically act to readmit the confederate states to the union?

The didn't. Once the rebellious states complied with the requirements placed on them by the Reconstruction Acts they had there delegations readmitted to Congress and not the states readmitted to the Union.

If they had no right to secede, then they never really left.

Bingo.

Also, if Virginia never left the union then the creation of the state of West Virginia, against the will of Virginia, would have been unconstitutional.

No. An organization of Virginia legislators who remained loyal to the U.S., and who coincidentally mainly came from western Virginia, got themselves recognized by Congress as the legitimate legislature. They voted to partition and Congress approved.

"An organization of Virginia legislators who remained loyal to the U.S., and who coincidentally mainly came from western Virginia, got themselves recognized by Congress as the legitimate legislature. They voted to partition and Congress approved."

Yes, but the Constitution specifically required the consent of Virginia. At least if Virginia was still a state.

"Section 3 - New States"
"New States may be admitted by the Congress into this Union; but no new States 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."

Lincoln's legal view was that there existed a state of insurrection, not war. That is an internal state of protest that does not reach International law level. (A rebellion does reach International Level, ergo other countries can take sides.) Lincoln's view was that the states had never left the union and were incapable of doing so. This angered the representatives of the extreme northern states who felt the southern states had dissolved and needed to be completely reconstituted and re-admitted into the union. In such a way, they could make various re admittance conditions. Lincoln was assassinated. Andrew Johnson continued Lincoln's views and was impeached because of it.