2016] FINDING CUSTOMARY INTERNATIONAL LAW 1895
to resolve issues such as whether piracy encompasses acts of aiding and
abetting,8 and whether it includes acts of violence that do not accompany a
robbery.9 Elsewhere, judicial efforts to discern custom are often necessary to
apply the so-called Charming Betsy canon, which requires a court to interpret
an ambiguous statute in a way that avoids conflict with international law.10
Finally, questions about CIL arise in constitutional interpretation. In
United States v. Bellaizac-Hurtado, for example, the government prosecuted
several foreign nationals under the Maritime Drug Law Enforcement Act
(“MDLEA”) for engaging in drug trafficking in the territorial waters of
Panama.11 In response, the defendants argued that the statutory prohibition
is unconstitutional—while Article I grants Congress the power to “define and
punish . . . Offences against the Law of Nations,”12 and while that power
confers authority to criminalize conduct that CIL prohibits,13 custom does not
prohibit drug trafficking.14 Persuaded by this argument, the court invalidated
the statute as applied and vacated the convictions.15
As a matter of international law and federal common law, it is clear what
courts should do when faced with these kinds of issues. The traditional
doctrine is that a rule of CIL arises from a “general and consistent practice of
states followed by them from a sense of legal obligation.”16 A correct analysis
would thus seek to answer two questions: first, is there a general and consistent
state practice on the given issue? And second, to the extent such a practice
exists, have states engaged in it out of a sense of international legal obligation
(otherwise known as opinio juris)? With respect to the first question, the
predominant view is that a practice cannot be “general” unless, at a minimum,
a “large share of [the] affected states” have engaged in it,17 that the
9. See United States v. Hasan, 747 F. Supp. 2d 599, 603, 640–41 (E.D. Va. 2010).
10. See Murray v. Schooner Charming Betsy, 6 U.S. (2 Cranch) 64, 118 (1804). See generally
Curtis A. Bradley, The Charming Betsy Canon and Separation of Powers: Rethinking the Interpretive Role
of International Law, 86 GEO. L.J. 479 (1998) (examining the canon’s origins and justifications).
United States v. Bellaizac–Hurtado, 700 F.3d 1245, 1247 (11th Cir. 2012).
12. U.S. CONST. art. I, § 8, cl. 10.
13. See Eugene Kontorovich, Discretion, Delegation, and Defining in the Constitutio n’s Law of
Nations Clause, 106 NW. U. L. REV. 1675, 1682 (2012) (“The originalist evidence strongly supports
the view that Congress can define only offenses that already exist in international law.”).
15. Id. at 1258. For other examples, see Zivotofsky v. Kerry, 135 S. Ct. 2076, 2084 (2015)
(relying in part on CIL to define the scope of the President’s recognition p ower), and Brown v.
United States, 12 U.S. (8 Cranch) 110 (1814) (using the law of nations in interpreting the
16. RESTATEMENT (THIRD) OF THE FOREIGN RELATIONS LAW OF THE UNITED STATES § 102
(AM. LAW INST. 1987); see also Bellaizac–Hurtado, 700 F.3d at 1252 (“We agree with our sister
circuits that customary international law is determined by examining state practice and opinio
juris . . . .”).
17. Andrew T. Guzman, Saving Customary International Law, 27 MICH. J. INT’L L. 115, 150
(2005); see also JAMES CRAWFORD, BROWNLIE’S PRINCIPLES OF PUBLIC INTERNATIONAL LAW 24 (8th
ed. 2012) (suggesting that CIL requires “substantial uniformity” in state practice).