Treaty commitments of the United States are of two kinds. In the language of Chief Justice Marshall in 1829: ”A treaty is, in its nature, a contract between two nations, not a legislative act. It does not generally effect, of itself, the object to be accomplished; especially, so far as its operation is intraterritorial; but is carried into execution by the sovereign power of the respective parties to the instrument.
”In the United States, a different principle is established. Our constitution declares a treaty to be the law of the land. It is, consequently, to be regarded in courts of justice as equivalent to an act of the legislature, whenever it operates of itself, without the aid of any legislative provision. But when the terms of the stipulation import a contract–when either of the parties engages to perform a particular act, the treaty addresses itself to the political, not the judicial department; and the legislature must execute the contract, before it can become a rule for the Court.” To the same effect, but more accurate, is Justice Miller’s language for the Court a half century later, in the Head Money Cases: ”A treaty is primarily a compact between independent nations. It depends for the enforcement of its provisions on the interest and the honor of the governments which are parties of it. . . . But a treaty may also contain provisions which confer certain rights upon the citizens or subjects of one of the nations residing in the territorial limits of the other, which partake of the nature of municipal law, and which are capable of enforcement as between private parties in the courts of the country.”