There is a fairly good argument that the surrender of citizenship was invalid under U.S. law–that Jefferson Davis was a citizen and a traitor when he made war on the U.S. government.
How? Let me answer in the form of a question:
Which office do you go to in the U.S. Courthouse in Richmond, Va., to give up your citizenship?
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The answer is that there is no such office. There is no way to voluntarily surrender U.S. citizenship while on U.S. soil. If you want to give up citizenship, the first thing you need to is leave the country.
I could (I won’t, because I have no reason to), yell as loudly as I want that I give up my citizenship, I could do so in the middle of the courthouse, I could do so in the face of a federal judge. I could sign a long, legal-sounding declaration to that extent. It wouldn’t matter a whit. I cannot give up my citizenship while still in the U.S.
Now, I might say that I’m not really in the U.S.–that my house, and the little lot it’s on, are the new state of Yoyodynia–and so I could give up my citizenship there. I think you can guess that I don’t think that matters–I have no right to have my house leave the Union-and so it remains U.S. soil.
As we’ve already discussed, I would argue that the U.S. constitution does not contain any provision that allows a state to legally secede. If that is true (and it is at least the position the Federal Government took), the south could not legally secede -and so any southerner trying to give up his citizenship would be trying to do so on U.S. soil. Hence, I would argue that means the attempt to give up citizenship wouldn’t have any effect. (IANAL, or even a legal historian, but my understanding is that the rule that you can’t give up citizenship of X while in X is fairly general–and would have applied in 1860).
The question of secession is not whether Jeff Davis (to pick one) had the right to leave, and no longer be governed by the Federal Government. I agree that he did. Where we disagree is whether he had a right to do so without leaving the territory of the United States–and specifically, whether he could legally take the State of Virginia, and the assorted state and Federal property therein with him.