It lies within the power of the United States government, either by treaty with a foreign power or by act of Congress, to confer citizenship on classes of persons without regard to birth or naturalization. Thus, when foreign territory is acquired by treaty, it is competent to provide in the treaty that the inhabitants of the territory by the fact of continuing to permanently reside within such territory become citizens. So it is competent for Congress to provide that on the division of land in an Indian reservation among the members of the Indian tribe to which the reservation is recognized as belonging, the Indians who accept their shares under such apportionment become citizens. (It has been so provided in acts of 1887 and other statutes.) When the independent state of Texas was admitted into the Union by act of Congress, the citizens of the state became citizens of the United States. It has even been suggested (in Boyd v. Thayer) that by the admission of a state into the Union which has previously had a territorial form of government, persons who were recognized by the territorial laws as possessing political privileges became citizens of the United States by virtue of the admission of the state, although they had been enjoying such political privileges without being citizens of the United States. Without attempting to specify all the methods of naturalization it is sufficient to say that citizenship by naturalization may be conferred by treaty or by statute, applicable to particular classes of persons, or by compliance on the part of any particular persons with the naturalization laws.

It still remains to be definitely determined whether by the acquisition of territory under a treaty which makes no provision as to citizenship, and without any act of Congress on the subject, the permanent inhabitants of such territory become citizens. It has, however, been settled that when foreign territory by treaty becomes territory of the United States, the persons permanently residing and continuing to reside therein whether they have become citizens or not are no longer aliens, and the statutes of the United States regulating immigrants from foreign countries are not applicable to such persons (Gonzales v. Williams).