Introduction

Transnational law, in Philip Jessup's classic definition, is ‘all law which regulates actions or events that transcend national frontiers’. This means that transnational law includes not only international law but much domestic law, and since international and domestic law often bear on the same subjects, questions about their relationship frequently arise. In the United States today, the relationship between Federal statutes and international law is well settled. According to section 115 of the Restatement (Third) of Foreign Relations Law of the United States, ‘An act of Congress supersedes an earlier rule of international law or a provision of an international agreement as law of the United States if the purpose of the act to supersede the earlier rule or provision is clear or if the act and the earlier rule or provision cannot be fairly reconciled’. US courts will interpret Federal statutes to avoid such violations, but in cases of clear conflict the later-in-time prevails.

It has not always been thus. At the time of the framing, the common understanding was that treaties were ‘beyond the lawful reach of legislative acts’. John Jay explained in The Federalist that as the consent of two nations was required to make treaties, ‘so must it ever afterwards be to alter or cancel them’. In a 2001 article, Detlev Vagts traced the judicial origins of the later-in-time rule for treaties to the mid-nineteenth century.