This Article explains what the law of nations meant at the time the United States was established and how it interacted with the original U.S. Constitution. The \u201claw of nations\u201d was not only a historical term for modern customary international law, it (1) was sometimes a broad term for all inter-national law, including conventions or treaties\u2014the \u201cconventional\u201d law of nations; (2) included principles of domestic law perceived to be shared by all civilized nations; (3) was a source of the U.S. law of federalism, given the early American view that the states retained residual sovereignty beyond what was conferred on the new general government by the Constitution; and (4) was perceived in part as unwritten natural law. The Americans who adopted the Constitution were keenly aware of their place in the world as a militarily weak new state in need of peace and trade with the European powers for survival, and thus eager to comply with the law of nations\u2014the intramural rules of the European world order. They recognized that the judicial branch could play an important role in advancing the new nation\u2019s inter-national acceptance and survival by judicious deployment of the law of nations as an instrument of U.S. foreign policy, which is why eight of the nine constitutional grants of judicial power in Article III implicated the law of nations. The law of nations was the original federal common law.<\/p>\n