So why is someone who’s never set foot in another nation subject to a foreign country?
Worldwide jurisdiction via nationality law.
Prime example:
The U.S. asserts JURISDICTION to tax on the basis of two factors: source of income, and citizenship. If a foreign individual or corporation receives income from a U.S. source, that income is subject to tax. If a U.S. citizen living abroad received income from a foreign source, that income is subject to tax merely because of the U.S. citizenship of the receiver. The IRS Office of Assistant Commissioner (International) has primary U.S. jurisdiction over overseas taxpayers.
Thus we have a perfect example of WORLDWIDE JURISDICTION over a country's citizens within a certain area: The U.S. taxes the foreign-source income of U.S. citizens living abroad.
The same principle applies to the U.K.'s birthright citizenship law (in Obama's case, the British Nationality Act of 1948). The U.K. had WORLDWIDE JURISDICTION to bestow automatic British citizenship at birth to any child born worldwide to a British father provided that the father of such a person is not a citizen of the U.K. by descent only.
Obama was born a Brit via his alien father. The DNC has already admitted that the British Nationality Act of 1948 "governed" (exact quote) his status. As such, Obama was NOT under the complete jurisdiction of the U.S. at birth, as required by the 14th Amendment and confirmed by the citizenship clause's author. Obama was born under the U.K.'s citizenship jurisdiction, both subject to a foreign power and owing allegiance to somebody else.
Neither was Obama's father permanently domiciled in the U.S. at the time of Obama's birth, so Gray's explicit ruling in U.S. v. Wong Kim Ark doesn't apply to him.