The national government under its incorporated powers operates under public international law. This is the spirit not the letter of the common law mixed with public Roman civil law, which is under the law of nations as expressed under Article 1 Section 8 clause 3 & 10 as well as Article 6 clause 2.
‘Doubtless Congress, in legislating for the territories, would be subject to those fundamental limitations in favor of personal rights which are formulated in the Constitution and its amendments, but those limitations would exist rather by inference and the general spirit of the Constitution, from which Congress derives all its powers, than by any express and direct application of its provisions.' Church of Jesus Christ of L. D. S. v. United States, 136 U.S. 1 , 34 L. ed. 478, 10 Sup. Ct. Rep. 792 [Bold emphasis added] See also, to the same effect First Nat. Bank v. Yankton County, 101 U.S. 129 , 25 L. ed. 1046; Murphy v. Ramsey, 114 U.S. 15 , 29 L. ed. 47, 5 Sup. Ct. Rep. 747.