26 USC § 4404
Territorial extent
October 30, 2020
The tax imposed by this subchapter shall apply only to wagers
(1) accepted in the United States, or
(2) placed by a person who is in the United States
(A) with a person who is a citizen or resident of the United States, or
(B) in a wagering pool or lottery conducted by a person who is a citizen or resident of the United States.