U.S. v. Wong Kim Ark
Some relevant excerpts:
In Inglis v. Sailors' Snug Harbor (1833), 3 Pet. 99,....Mr. Justice Thompson, speaking for the majority of the court, said:
"It is universally admitted, both in the English courts and in those of our own country, that all persons born within the Colonies of North America, whilst subject to the Crown of Great Britain, are natural-born British subjects."
" It was contended by one of the learned counsel for the United States that the rule of the Roman law, by which the citizenship of the child followed that of the parent, was the true rule of international law, as now recognized in most civilized countries, and had superseded the rule of the common law, depending on birth within the realm, originally founded on feudal considerations.
But at the time of the adoption of the Constitution of the United States in 1789, and long before, it would seem to have been the rule in Europe generally, as it certainly was in France, that, as said by Pothier, "citizens, true and native-born citizens, are those who are born within the extent of the dominion of France,"...
There is, therefore, little ground for the theory that, at the time of the adoption of the Fourteenth Amendment of the Constitution of the United States, there as any settled and definite rule of international law, generally recognized by civilized nations, inconsistent with the ancient rule of citizenship by birth within the dominion.
The foregoing considerations and authorities irresistibly lead us to these conclusions:
the Fourteenth Amendment affirms the ancient and fundamental rule of citizenship by birth within the territory, in the allegiance and under the protection of the country, including all children here born of resident aliens, with the exceptions or qualifications (as old as the rule itself) of children of foreign sovereigns or their ministers, or born on foreign public ships, or of enemies within and during a hostile occupation of part of our territory, and with the single additional exception of children of members of the Indian tribes owing direct allegiance to their several tribes.
The Amendment, in clear words and in manifest intent, includes the children born, within the territory of the United States, of all other persons, of whatever race or color, domiciled within the United States. Every citizen or subject of another country, while domiciled here, is within the allegiance and the protection, and consequently subject to the jurisdiction, of the United States. His allegiance to the United States is direct and immediate, and, although but local and temporary, continuing only so long as he remains within our territory, is yet, in the words of Lord Coke in Calvin's Case, 7 Rep. 6a, "strong enough to make a natural subject, for if he hath issue here, that issue is a natural-born subject;" and his child, as said by Mr. Binney in his essay before quoted, "if born in the country, is as much a citizen as the natural-born child of a citizen, and by operation of the same principle." It can hardly be denied that an alien is completely subject to the political jurisdiction of the country in which he resides .....