Chicago Journal of International Law

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It is well established that there is a consensus, two-element approach to the identification of customary international law. Among international courts and organizations, a customary rule is identified based on evidence of a general practice by states, which is accepted as law. Customary international law, however, is also subject to identification at the national level. For centuries, questions regarding the existence and content of customary international rules have arisen in national courts. Given their own institutionalized methods of resolving legal ambiguity, national courts are thus routinely faced with a normative conflict: is the appropriate method for identifying rules of customary international law located in the national or international realm? By using customary international law as a case study, this Article offers a more nuanced understanding of how international law is localized into U.S. courts. While prevailing theories posit that the diffusion of international rules results in national acceptance or rejection, this empirical analysis demonstrates how normative pluralism may also generate hybridization. As international integration accelerated after World War II, U.S. judges increasingly relied on hybrid models of decision-making that sought legitimacy within both the national and international legal systems.

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