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32 U. S., at 566; accord, La Abra Silver Mining Co. v. United States, 175 U. S. 423, 460 (1899); 1 W. Blackstone, Commentaries on the Laws of England 90 (1765) (Blackstone). Whatever number of treaties remain in force, they cannot justify ICWA.

Third, the Commerce Clause cannot support ICWA. As originally understood, the Clause confers a power only over buying and selling, not family law and child custody disputes. Even under our more modern, expansive precedents, the Clause is still limited to only “economic activity” and cannot support the regulation of core domestic matters like family or criminal laws. See Lopez, 514 U. S., at 560; United States v. Morrison, 529 U. S. 598, 610–611 (2000); National Federation of Independent Business v. Sebelius, 567 U. S. 519, 552 (2012) (opinion of ); id., at 657 (Scalia, J., dissenting). And even Kagama itself rejected the Commerce Clause as a basis for any sort of expansive power over Indian affairs. 118 U. S., at 378–379. Therefore, nothing about that Clause supports a law, like ICWA, governing child custody disputes in state courts.

Fourth, the Federal Government’s foreign-affairs powers cannot support ICWA. For today’s purposes, I will assume that some tribes still enjoy the same sort of pre-existing sovereignty and autonomy as tribes at the Founding, thereby establishing the sort of quasi-foreign, government-to-government relationship that appears to have defined those powers at the Founding. Even so, the foreign-affairs