Code Section 7701 (a)(30)
U.S citizens are U.S Persons and Citizens of foreign countries are U.S Persons who meet either of the following two tests:
Green Card test
Substantial...
Foreign Corporations and non-resident aliens who have a U.S source income are subject to U.S Taxation.
According to codes section 871 (b) and 882, all Foreign Persons are taxed at...