Exception: American Samoa Explained

American Samoa is a U.S. possession listed under U.S. Code Title 48, Chapter 13:

https://www.law.cornell.edu/uscode/text/48/chapter-13

Their citizenship status at birth is described in 8 U.S.C. §1408. The authority to control the citizenship status is contained in Constitution Article 4, Section 3, Clause 2:

The Congress shall have power to dispose of and make all needful rules and regulations respecting the territory or other property belonging to the United States; and nothing in this Constitution shall be so construed as to prejudice any claims of the United States, or of any particular state.

[U.S. Const. art. IV, § 3, cl. 2.]

In the case of American Samoans:

Political status=non-citizen national status + Allegiance.