Someone that doesn’t have any citizenship of any country is “stateless” and is in a world of pain.
Presumably the only reason that the US would in practise revoke citizenship is for fighting for a foreign army, in which that person would have the citizenship of another country and thus not end up stateless.
It seems that recently the US did try and revoke citizenship of one person that fought for the Taliban in Afghanistan and the courts overturned it. In the end they did a deal where he voluntarily renounced his citizehship in order to be released:
I know one person who did renounce US citizenship in 1969. He lived in Detroit. Draft notice in hand, he crossed the river to Windsor, got on the first train to Montreal and went to the US consulate to renounce his citizenship. (It was real easy to get a Canadian immigration visa in those days.) Even then, someone counseled him against it and he had to sign all sorts of papers. Until he could become a Canadian citizen, he had to travel on something called, I believe, a Nansen passport, which required him to get visas for any country he visited. He was under indictment in the US, although that was eventually dropped and he travels freely to the US and other countries.
Even then, it was not so easy to renounce. Even becoming a citizen did not automatically result in renunciation. It helped that Canada did not require renunciation of other citizenships.
So, the answer to OP is that the law says the US government can NOT “revoke” birth citizenship of its own initiative: * the individual* has to act in such a manner as to give it up, and then the government can officially point out that s/he has done so; and it’s not easy.
In real-world terms the various laws and requirements many countries impose to affirm that you renounce other allegiances in the process of claiming theirs are often viewed as something of a ceremonial formality, because a whole lot of other countries simply chose to disregard them and continue to consider you a citizen anyway. Problem is, it’s the respective Foreign Offices that make that determination, not the citizens. After the Terrazas case, as mentioned, new rules were issued that the US will disregard “routine” oaths of allegiance, and a renunciation of citizenship has to be* directed to the US government*, not to the other country’s. And even then they reserve the right to look into what is it you actually DO, to determine if it sticks.
Herbert Hoover, deported “back to their country” several thousands Mexican Americans (born Americans with Mexican origins). I dont know if they lost their American citizenship in the process, but they were treated as if they didnt have any.
There does remain the question as to what citizenship a person then has. Clearly the majority of the above cases are about someone electing to become a de-facto citizen of another nation. But not all. In some ways this reflects the modern political landscape. The advent of organisations that attack sovereign nations that are not themselves nations is not something that the system seems well set up to cope with. You can commit a lot of offences against the US as a single acting person, or member of a non-sovereign nation organisation. If you avowed that you did so with intent to lose citizenship - well it looks as if you might become stateless. Something that the world in general doesn’t cope all that well with. Indeed, imagine you lost citizenship, to where might you be deported? Or indeed, it you did go somewhere, and you committed some other offence, and got yourself deported, where would they send you? I bet back to the US. Who would be in a curious situation. (Not so curious as you however.)