The majority opinion in this Supreme Court case, 299 U.S. 304 (1936), upheld an embargo on arms destined for Paraguay and Bolivia, two nations at war. Justice George Sutherland's majority opinion included the following statements:
It will contribute to the elucidation of the question if we first consider the differences between the powers of the federal government in respect of foreign or external affairs and those in respect of domestic or internal affairs. That there are differences between them, and that these differences are fundamental, may not be doubted. The two classes of powers are different, both in respect of their origin and their nature. The broad statement that the federal government can exercise no powers except those specifically enumerated in the Constitution, and such implied powers as are necessary and proper to carry into effect the enumerated powers, is categorically true only in respect of our internal affairs….
It results that the investment of the federal government with the powers of external sovereignty did not depend upon the affirmative grants of the Constitution. The powers to declare and wage war, to conclude peace, to make treaties, to maintain diplomatic relations with other sovereignties, if they had never been mentioned in the Constitution, would have vested in the federal government as necessary concomitants of nationality….
Not only, as we have shown, is the federal power over external affairs in origin and essential character different from that over internal affairs, but participation in the exercise of the power is significantly limited. In this vast external realm, with its important, complicated, delicate and manifold problems, the President alone has the power to speak or listen as a representative of the nation….
It is important to bear in mind that we are here dealing not alone with an authority vested in the President by an exertion of legislative power, but with such an authority plus the very delicate, plenary and exclusive power of the President as the sole organ of the federal government in the field of international relations.