[Cboldt]

-- If two people were born in Guam IN 1953 (ACCORDING TO THE LAW YOU POSTED) to American citizens who were citizens of Guam, are those two people American citizens at the moment of their birth? --

Yes. I would add that the parents do not have to be US citizens. They can be citizens of any country. The parents are required to be subject to the jurisdiction of the United States. That is not the same as US citizen.

[House Atreides]

— If two people were born in Guam IN 1953 (ACCORDING TO THE LAW YOU POSTED) to American citizens who were citizens of Guam, are those two people American citizens at the moment of their birth? -
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Yes. I would add that the parents do not have to be US citizens. They can be citizens of any country. The parents are required to be subject to the jurisdiction of the United States. That is not the same as US citizen.
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OK, these two American citizens (since birth in 1953), let’s call them Joseph & Mary, get married and have one child born in Guam and a second child born in Hawaii and a third child born in Pennsylvania. Are all three of Joseph & Mary’s children American citizens from the moment they are born?

[erkelly]

Excuse me, but subject to the jurisdiction of a country, does indeed mean that person is a citizen of that country, and no other (unless a dual citizen in which he can subject to jurisdiction of both.) People often get subject to jurisdiction and subject to law mixed up. If you are living in another country, you are indeed subject to its laws and can get yourself deported, imprisoned, or fined (or all three) if you break those laws; you may be liable for some taxes. You are not under their jurisdiction, however. You are not issued a passport that country, you do not vote in their elections, you are not ordinarily subject to any taxes of that nation (unless you physically present in that country or hold property there, in which case you may have some tax liability) you are not required to serve in their military, you do not have the protection of that country’s embassy/consul when abroad, for examples.