The U.S. Supreme Court held that all extensive regulation of foreign affairs by a state is prohibited, either by implicit preemption or simply because the states lack the authority to delve too deeply into international matters in:

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Crosby v. National Trade Council dealt with the issue of state regulation in foreign affairs, where the Supreme Court held that state laws interfering with federal foreign policy are preempted.

The US Supreme Court Held That All Extensive Regulation of Foreign