¹ see Statute of the International Court of Justice, Art. 38(1)(b), June 26, 1945, 59 Stat. 1055, 33 UNTS 993; American Law Institute, Restatement (Third) Of the Foreign Relations Law of the United States §102(2) (1986) [hereinafter Third Restatement]. The statute, decisions, and other materials pertaining to the International Court of Justice (ICJ) are available on the court’s website, http://www.cij-icj.org.

² See, e.g., Andrew T. Guzman, How International Law Works 183–84 (2008). The International Law Commission (ILC) recently included the topic “formation and evidence of customary international law” in its research program. see Michael Wood, Formation and Evidence of Customary International Law (Annex A to the Report of the International Law Commission on the Work of Its Sixty-third Session, UN GAOR, 66th Sess., Supp. No. 10, at 305, UN Doc. A/66/10 (2011)); Reportofthe International Law Commission on the Work of Its Sixty-fourth Session, UN GAOR, 67th Sess., Supp. No. 10, at 108, UN Doc. A/67/10 (2012). Documentsof the International Law Commission are available on its website, http://www.un.org/law/ilc/.

³ See, e.g., Jack L. Goldsmith & Eric A. Posner, The Limits of International Law (2005); Dunbar, N. C. H., The Myth of Customary International Law, 1983 Australian Y.B. Int’l L. 1, 2Google Scholar; Kelly, J. Patrick, The Twilight of Customary International Law, 40 Va. J. Int’l L. 449, 451 (2000)Google Scholar; Reisman, W. Michael, The Cult of Custom in the Late 20th Century, 17 Cal. W. Int’l L.J. 133 (1987)Google Scholar; Trimble, Phillip R., A Revisionist View of Cus tomary International Law, 33 UCLA L. Rev. 665, 709 (1986)Google Scholar.

⁴ See, e.g., Goldsmith, Jack L. & Posner, Eric A., A Theory of Customary International Law, 66 U. Chi. L. Rev. 1113, 1115 (1999)CrossRefGoogle Scholar (“The case studies... suggest that the behaviors associated with CIL do not reflect a unitary underlying logic, and that CIL does little apparent work in guiding national behavior.”).

⁵ see Goldsmith & Posner, supra note 3, at 25–26; Guzman, supra note 2, at 184.

⁶ see Goldsmith & Posner, supra note 3; Guzman, supra note 2; Chinen, Mark A., Game Theory and Customary International Law: A Response to Professors Goldsmith and Posner, 23 Mich. J. Int’l L. 143 (2001)Google Scholar; Goldsmith & Posner, supra note 4; Guzman, Andrew T., Saving Customary International Law, 27 Mich. J. Int’l L. 115(2005)Google Scholar; Norman, George & Trachtman, Joel P.,The Customary International Law Game, 99 AJIL 541(2005)CrossRefGoogle Scholar; Parisi, Francesco & Fon, Vincy, International Customary Law and Articulation Theories: An Economic Analysis, 2 Int’l L. & Mgmt. Rev. 1 (2006)Google Scholar; Swaine, Edward T., Rational Custom, 52 Duke L.J. 559 (2002)CrossRefGoogle Scholar.

⁷ see Guzman, supra note 2, at 33–48.

⁸ See id. at 193; Goldsmith & Posner, supra note 4, at 1120; Norman & Trachtman, supra note 6, at 544–48. This point is made in Kingsbury, Benedict, The Concept of Compliance as a Function of Competing Conceptions of International Law, 19 Mich. J. Int’l L. 345, 354 (1998)Google Scholar.

⁹ See, e.g., Goldsmith & Posner, supra note 3, at 40–42; Norman & Trachtman, supra note 6, at 572.

¹⁰ See, e.g., Goldsmith & Posner,supra note 3, at 25 (“Despite the many disagreements within the traditional paradigm, the parties to this debate assume that customary International Law is unitary, universal, and exogenous.... Our theory of customary International Law challenges each of these assumptions.”); Guzman, supra note 2, at 184 (“Some of the standard views of CIL cannot be reconciled with the theory presented here or any other theory of rational states. These elements of CIL, therefore, must be rethought or discarded if we are to understand how CIL influences states.”)

¹¹ See infra note 73 and accompanying text.

¹² Verdier, Pierre-Hugues & Voeten, Erik, How Does Customary International Law Change? The Case of State Immunity, 58 Int’l Stud.Q.(forthcoming) Google Scholar. In 2008, Andrew Guzman could state: “Because we do not have any reliable empirical evidence about the actual impact of CIL, virtually all inquiries into CIL... have focused on the theoretical side.” Guzman, supra note 2, at 207. On the lack of empirical scholarship on CIL, see also Abbott, Kenneth W. & Snidal, Duncan, Law, Legalization and Politics: An Agenda for the Next Generation of IL/IR Scholars, in Interdisciplinary Perspectives on International Law and International Relations 33 (Dunoff, Jeffrey L. & Pollack, Mark A. eds., 2013)Google Scholar. While our empirical article (cited above) outlines our theory of CIL, this article develops it in much greater detail, draws on additional examples, and explores its implications for CIL doctrine.

¹³ On the distinction between direct and diffuse reciprocity, see Keohane, Robert O., Reciprocity in International Relations, 40 Int’l Org. 1 (1986)CrossRefGoogle Scholar.

¹⁴ See, e.g., Benvenisti, Eyal, Customary International Law as a Judicial Tool for Promoting Efficiency, in The Impact of International Law on International Cooperation: Theoretical Perspectives 85 (Benvenisti, Eyal & Hirsch, Moshe eds., 2004)CrossRefGoogle Scholar; Kontorovitch, Eugene, Inefficient Customs in International Law, 48 Wm. & Mary L. Rev. 859 (2006)Google Scholar; Meyer, Timothy, Codifying Custom, 160 U. Pa. L. Rev. 995, 1050 (2012)Google Scholar.

¹⁵ Not all International Law rules are prisoner’s dilemmas: some may reflect coincidence of interests (where the CIL rule simply reflects the actions that states would independently take in any event) or simple coordination games (where states benefit from a common rule and have no incentives to defect). see Goldsmith & Posner, supra note 3, at 26–35(2005); Guzman,supra note 2, at 25–29. The prisoner’s dilemma is often used, however, to model more difficult international cooperation problems. If international law can sustain a cooperative equilibrium in such circumstances, one can more readily conclude that it has an impact on state behavior. See id. at 29–30; Norman & Trachtman, supra note 6, at 548–51 (2005). Part III, infra, explores the application of our theory to CIL rules that are not prisoner’s dilemmas.

¹⁶ Guzman, supra note 2, at 33, refers to these mechanisms as the “Three Rs” of compliance.

¹⁷ Id. at 33.

¹⁸ Id. at 42–45.

¹⁹ See, e.g., Robert Axelrod, The Evolution of Cooperation (1984).

²⁰ Guzman, supra note 2, at 34, 46–49.

²¹ The reason is that in many cases, unilateral action will not exact a significant cost from the breaching state. Thus, economic sanctions are often ineffective when they lack broad international support, as they merely divert trade from the sanctioning state to others. see Drezner, Daniel W., Bargaining, Enforcement, and Multilateral Sanctions: When Is Cooperation Counterproductive?, 54 Int’l Org. 73 (2000)CrossRefGoogle Scholar.

²² see Keohane, supra note 13.

²³ see Brewster, Rachel, Unpacking the State’s Reputation, 50 Harv. Int’l L.J. 231 (2009)Google Scholar; Downs, George W. & Jones, Michael A., Reputation, Compliance and International Law, 31 J. Legal Stud. S95 (2002)CrossRefGoogle Scholar.

²⁴ Guzman, supra note 2, at 34–41; see also Michael Tomz, Reputation and International Cooperation: Sovereign Debt Across Three Centuries (2007).

²⁵ see Goldsmith & Posner, supra note 3, at 29–32.

²⁶ See id. at 35–38.

²⁷ See id. at 40–42.

²⁸ See id. at 25.

²⁹ See id. at 40–42.

³⁰ see Norman & Trachtman, supra note 6, at 545.

³¹ These parameters include the relative value of cooperation and defection, the number of states, the availability of information, the discount factors of states, and the expected duration and frequency of interactions. Id. at 567–68.

³² Guzman, supra note 2, at 42, 63–69, 190–94; see also Swaine, supra note 6, at 617.

³³ Guzman, supra note 2, at 208–09.

³⁴ Bates, Robert H., De Figueiredo, Rui J. P. Jr. & Weingast, Barry R., The Politics of Interpretation: Rationality, Culture, and Transition, 26 Pol. & Soc’y 603, 630 (1998)Google Scholar.

³⁵ Hadfield, Gillian K. & Weingast, Barry R., What Is Law? A Coordination Model of the Characteristics of Legal Order, 4 J. Legal Analysis 471, 476 (2012)CrossRefGoogle Scholar.

³⁶ General Agreement on Tariffs and Trade, Art.XX, Marrakesh Agreement Establishing the World Trade Organization, Apr. 15, 1994, 1867 UNTS 154, Annex 1A, 1867 UNTS 187, reprinted in The Results of the Uru Guay Round of Multilateral Trade Negotiations: The Legal Texts 17, 455 (1999), 33 ILM 1153 (1994).

³⁷ Another important example is the inclusion in many human rights treaties of clauses allowing states to derogate from protected rights in times of public emergency, see, e.g., International Covenant on Civil and Political Rights, Art. 4(1), Dec. 16, 1966, 999 UNTS 171, or specifying permissible derogations from specific rights, see, e.g., European Convention on Human Rights, Art. 10(2), Nov. 4, 1950, 213 UNTS 222.

³⁸ See, e.g., Laurence R. Helfer, Flexibility in International Agreements, in Interdisciplinary Perspectives on International Law and International Relations, supra note 12, at 175; Koremenos, Barbara, Lipson, Charles & Snidal, Duncan, The Rational Design of International Institutions, 55 Int’l Org. 761 (2001)CrossRefGoogle Scholar; Koremenos, Barbara, Contracting Around International Uncertainty, 99 Am. Pol. Sci. Rev. 549 (2005)CrossRefGoogle Scholar.

³⁹ Some scholars also argue that by allowing states that face strong pressure to breach a WTO obligation and, in effect, to pay a penalty for doing so, this system facilitates efficient breach. see Posner, Eric A. & Sykes, Alan O., Efficient Breach of International Law: Optimal Remedies, Legalized Noncompliance, and Related Issues, 110 Mich. L. Rev. 243 (2011–12)Google Scholar; Sykes, Alan O., Protectionism as a “Safeguard:” A Positive Analysis of the GATT “Escape Clause” with Normative Speculations, 58 U. Chi. L. Rev. 255 (1991)CrossRefGoogle Scholar.

⁴⁰ see Articles on Responsibility of States for Internationally Wrongful Acts, in Report of the International Law Commission on the Work of Its Fifty-third Session, UNGAOR 56th Sess.,Supp.No.10, at 43, UN Doc.A/56/10 (2001) [hereinafter ILC Articles on State Responsibility], reprinted in Crawford, James, The International Law Commission’s Articles on State Responsibility:Introduction, Text and Commentaries 61 (2002)Google Scholar.

⁴¹ Gabčíkovo-Nagymaros Project (Hung./Slovk.), 1997 ICJ Rep. 7, para. 51 (Sept. 25).

⁴² These arbitral decisions and the annulment proceedings that followed several of them are described and debated in anabundant literature.See, e.g., Alvarez, José E., The Return of the State, 20 Minn. J. Int’l L. 223 (2011)Google Scholar. It should be noted that, narrowly drafted as it is, Article 25 has been criticized as too broad to accurately reflect pre- 2001 customary international law, which recognized a necessity defense only in circumstances that threatened a state’s very existence. see Sloane, Robert D., On the Use and Abuse of Necessity in the Law of State Responsibility, 106 AJIL 447 (2012)CrossRefGoogle Scholar. Likewise, contrary to Article 25, Brownlie argued in the sixth, 2003 edition of his treatise that “necessity as an omnibus category probably does not exist.” Brownlie, Ian, Principles of Public International Law 448 (6th ed. 2003)Google Scholar; see also Bodansky, Daniel & Crook, John R., Introduction and Overview, 96 AJIL 773, 788 (2002)CrossRefGoogle Scholar (introduction to symposium on ILC Articles on State Responsibility).

⁴³ In some circumstances, flexibility may exist because the applicable CIL rule is unclear or lacks detail. Such flexibility does not provide, however, the same cooperation-enhancing benefits as formal flexibility clauses, under which limited breach is clearly deemed permissible under certain conditions. By contrast, an attempt to justify a breach by reference to the rule’s ambiguity is likely to be interpreted as a violation by the counterparty and (some) third parties.

⁴⁴ ILC Articles on State Responsibility, supra note 40, Art. 49(2).

⁴⁵ Crawford, supra note 40, at 284.

⁴⁶ see Bederman, David J., Counterintuiting Countermeasures, 96 AJIL 817, 822 (2002)CrossRefGoogle Scholar.

⁴⁷ ILC Articles on State Responsibility, supra note 40, Art. 51.

⁴⁸ Id., Art. 50.

⁴⁹ Id., Art. 52.

⁵⁰ Id., Art. 49(3).

⁵¹ According to David Caron, the “articles are a mix of codification and progressive development; to be frank, it would often be difficult to say which article partakes more of one or the other.” Caron, David D., The ILC Articles on States Responsibility: The Paradoxical Relationship Between Form and Authority, 96 AJIL 857, 873 (2002)CrossRefGoogle Scholar; see also Sloane, supra note 42, at 451. The codification of state responsibility took more than forty years, and the provisions on countermeasures were among the most controversial and debated. see Crawford, supra note 40, at 47–49; Bederman, supra note 46.

⁵² see Dispute Settlement Rules: Understanding onRules and Procedures Governing the Settlement of Disputes, Art. 22, Marrakesh Agreement Establishing the World Trade Organization, Apr. 15, 1994, 1867 UNTS 154, Annex 2, 1869 UNTS 401, reprinted in The Results of the Uruguay Round of Multilateral Trade Negotiations, supra note 36, at 354 (1999), 33 ILM 1226 (1994).

⁵³ In addition to Article 51’s vague proportionality rule, commentators have pointed to the ILC Articles’ wide spread use of imprecise concepts. see Bodansky & Crook, supra note 42, at 789.

⁵⁴ For our discussion of the role of international courts and tribunals in CIL, see subsection “International Courts” below.

⁵⁵ The principle of relative effect of treaties is reflected in Article 34 of the Vienna Convention on the Law of Treaties, opened for signature May 23, 1969, 1155 UNTS 331.

⁵⁶ North Sea Continental Shelf (Ger./Den.; Ger./Neth.), 1969 ICJ REP. 3, para. 63 (Feb. 20).

⁵⁷ See, e.g., Thirlway, Hugh, The Sources of International Law, in International Law 95, 106 (Evans, Malcolm D. ed., 3d ed. 2010)CrossRefGoogle Scholar. The discussion here is limited to general CIL, although traditional doctrine recognizes regional and special CIL in some circumstances.

⁵⁸ Lauterpacht, Hersch, The Problem of Jurisdictional Immunities of Foreign States, 1951 Brit. Y.B. Int’l L. 220, 228Google Scholar.

⁵⁹ Dollfus Mfg. v. Bank of England, [1952] A.C. 582, 613 (H.L.).

⁶⁰ see Hilton v. Guyot, 159 U.S. 113 (1895) (arguing that the reciprocal recognition of other states’ judgments is evidence that such recognition is a matter of the “comity of nations”); see also Michaels, Ralf, Recognition and Enforcement of Foreign Judgments, in Max Planck Encyclopedia of Public International Law, para. 11 (Wolfrum, Rudiger ed., online ed. 2008), at http://www.mpepil.com Google Scholar.

⁶¹ see Report of the International Law Commission to the General Assembly, UNGAOR, 13th Sess., Supp. No. 9, UN Doc. A/3859 (1958),reprinted in [1958]2 Y.B. Int’lL. Comm’n 78, 100, UN Doc. A/CN.4/SER.A/1958/Add.1; Ling, Yu-Long, A Comparative Study of the Privileges and Immunities of United Nations Member Representatives and Officials with the Traditional Privileges and Immunities of Diplomatic Agents, 33 Wash. & Lee L. Rev. 91, 111–12 (1976)Google Scholar.

⁶² see Report of the International Law Commission to the General Assembly, supra note 61, at 100.

⁶³ see Frederick Schauer, Thinking Like a Lawyer (2009).

⁶⁴ see Bradley, Curtis A. & Morrison, Trevor W., Presidential Power, Historical Practice, and Legal Constraint, 113 Colum. L. Rev. 1097, 1132–37 (2013)Google Scholar; Koh, Harold Hongju, The State Department Legal Adviser’s Office: Eight Decades in Peace and War, 100 Geo. L.J. 1747 (2012)Google Scholar; Stephan, Paul B., Privatizing International Law, 97 Va. L. Rev. 1573, 1641 (2011)Google Scholar.

⁶⁵ There are, to be sure, exceptions. See Goldsmith & Posner, supra note 3, which provides several examples, primarily from the law of war at sea, where purported CIL rules were applied inconsistently across states and over time. These examples are discussed in part III.

⁶⁶ For example, in the early 1920s, Italy—which had adopted restrictive immunity decades before—successfully claimed immunity in the United States for a state-owned ship engaged in commerce. Berizzi Bros. Co. v. S.S. “Pesaro,” 271 U.S. 562 (1926).

⁶⁷ Although Polish courts purported to apply absolute immunity on a reciprocal basis, they did not succeed in doing so, and actually ended up applying absolute immunity even to foreign states that had clearly switched to restrictive immunity. see Verdier & Voeten, supra note 12.

⁶⁸ For example, the terrorism exception in the Foreign Sovereign Immunity Act, 28 U.S.C. §§1330, 1332(a)(4), 1391(f), 1441(d), 1602–1611, is arguably a countermeasure against state sponsors of terrorism. Putting the exception in place required statutory amendments, however, and its use requires a presidential designation—a political decision of the highest order that is not available to punish routine International Law violations.

⁶⁹ see Verdier & Voeten, supra note 12.

⁷⁰ Guzman, supra note 2, at 209.

⁷¹ see Brewster, supra note 23; Downs & Jones, supra note 23.

⁷² Guzman, supra note 2, at 208.

⁷³ Charney, Jonathan I., The Persistent Objector Rule and the Development of Customary International Law, 1985 Brit. Y.B. Int’l L. 1, 21Google Scholar; see also Military and Paramilitary Activities in and Against Nicaragua (Nicar. v. U.S.), 1986 ICJ Rep. 14, para. 207 (June 27) (“Reliance by a State on a novel right or an unprecedented exception to the principle might, if shared in principle by other States, tend towards a modification of customary international law.”); Rosalyn Higgins, Problems and Process 19 (1994) (“One of the special characteristics of International Law is that violations of law can lead to the formation ofnew law.”); Bradley, Curtis A. & Gulati, Mitu,Withdrawing from International Custom, 120 Yale L.J. 202, 212 (2010)Google Scholar (“The only way for nations to change a rule of CIL (as opposed to overriding it by treaty) is to violate the rule and hope that other nations accept the new practice.”); Glennon, Michael, How International Rules Die, 93 Geo. L.J. 939, 957 (2005)Google Scholar (“[C]ustomary International Law is thought to be altered by acts that initially constitute violations of old rules; that is how it changes.”).

⁷⁴ To be sure, a party affected by the violation may in some circumstances suspend or terminate the treaty, but this option must be exercised affirmatively by the party in question and is exceptional, especially in the case of multilateral treaties that articulate general rules analogous to the sort of general CIL that we are concerned with here. Also, in extreme circumstances a treaty may fall into desuetude. see Dinstein, Yoram, The Interaction Between Customary International Law and Treaties, 322 Recueil Des Cours 243, 411–15 (2006)Google Scholar. But that is highly unusual.

⁷⁵ see Charney, Jonathan I.,The Power of the Executive Branch of the United States Government to Violate Customary International Law, 80 AJIL 913, 916 (1986)CrossRefGoogle Scholar; Meron, Theodor,The Geneva Conventions as Customary Law, 81 AJIL 348, 369 (1987)CrossRefGoogle Scholar.

⁷⁶ In cases where the decision is made by a court, the balancing exercise could be described as one between the court’s propensity to expand its jurisdiction (in this case by denying immunity) and its concern with the foreign policy implications of its decision. Courts are often concerned with such implications, leading to the use of various avoidance doctrines to dismiss cases involving foreign states or International Law breaches. For a classic statement, see Banco Nacional de Cuba v. Sabbatino, 376 U.S. 398 (1964).

⁷⁷ See supra notes 70–72 and accompanying text.

⁷⁸ Of course, this effect will be much attenuated in areas where state practice is not public or when violations are easy to dissimulate. For these, precedential concerns are unlikely to have much of an effect, except in those rare cases in which the violation is exposed. This problem is not unique to our theory, however: the other compliance mech anisms described above—reciprocity, retaliation, and reputation—also cannot have much impact if the violation is not known by other states.

⁷⁹ In some circumstances a state may not value the cooperative rule at all; that is, the state is not merely looking to free ride but would genuinely prefer that all states adopted a different rule. In such cases, defecting should be an obvious choice unless other states are able to implement retaliation strategies or the reputational costs are very high. Unlike for other defections, we would expect the state to attempt to maximize the precedential impact of its decision—for instance, by making a clear declaration that it believes the CIL rule has fundamentally changed rather than asserting a small modification or exception to the rule.

⁸⁰ see Thomas C. Schelling, Micromotives and Macro Behavior 83–110(1978); Granovetter, Mark, Threshold Models of Collective Behavior, 83 Am. J. Soc. 1420 (1978)CrossRefGoogle Scholar; Schelling, Thomas C., Dynamic Models of Segregation, 1 J. Mathematical Soc. 143 (1971)CrossRefGoogle Scholar.

⁸¹ see Verdier & Voeten, supra note 12, Figure 1.

⁸² Trendtex Trading Corp. v. Cent. Bank of Nigeria, [1977] 1 Q.B. 529, 556 (C.A.).

⁸³ see Heizen, Bernard G., The Three-Mile Limit: Preserving the Freedom of the Seas, 11 STAN. L. Rev. 597, 618–19, 629–51 (1959)CrossRefGoogle Scholar. Several authors point out that states’ claims varied to some extent, with some claiming slightly broader four-or six-(nautical) mile territorial seas and some claiming exceptions such as contiguous zones to prevent smuggling. See, e.g., Crawford, James, Brownlie’s Principles of Public International Law 255, 259–60 (8th ed. 2012)CrossRefGoogle Scholar; Goldsmith & Posner, supra note 3, at 59–66; Heizen, supra. For our purposes, it is sufficient that the three-mile rule was widely accepted and that, in any event, even the states that claimed somewhat broader territorial seas accepted limitations that were much more restrictive than the claims later made by the mid-twentieth-century defectors—for example, a fifty-mile exclusive fishing zone in the case of Iceland. see Fisheries Jurisdiction (UK v. Ice.), 1974 ICJ Rep. 3 (July 25).

⁸⁴ see Charney, supra note 73, at 11.

⁸⁵ See id. at 13; Heizen, supra note 83, at 597, 640–41; Stein, Ted L., The Approach of the Different Drummer: The Principle of the Persistent Objector in International Law, 26 Harv. Int’l L.J. 457, 462 (1985)Google Scholar.

⁸⁶ Heizen, supra note 83, reports that by the 1958 Law of the Sea Conference, twenty-seven states claimed territorial seas broader than twelve miles.

⁸⁷ The United Kingdom and United States adopted twelve-mile zones in the 1980s. see Crawford, supra note 83, at 260; Akehurst, Michael, Custom as a Source of International Law, 1975 Brit. Y.B. Int’l L. 1,27 Google Scholar(“The United Kingdom thus suffered all the disadvantages of upholding the three-mile limit, without enjoying any of the advantages in practice—a situation which eventually induced the United Kingdom to claim, with some exceptions, a twelve-mile exclusive fishing zone.”). On Japan, see Charney, supra note 73, at 12. Eventually, the UN Convention on the Law of the Sea codified a twelve-mile rule for the territorial sea anda 200-mile exclusive economic zone (EEZ) that confers extensive rights to the coastal state. see UN Convention on the Law of the Sea, opened for signature Dec. 10, 1982, 1833 UNTS 397. Both of these regimes are now widely recognized as CIL. See infra note 197.

⁸⁸ Thus, the “United States has long maintained that a taking of property for public purposes is contrary to international law unless it is accompanied by ‘prompt, adequate and effective compensation,’ a formulation often attributed to U.S. Secretary of State Cordell Hull.” Damrosch, Lori F., Henkin, Louis, Murphy, Sean D. & Smit, Hans, International Law 1080 (5th ed. 2009)Google Scholar. By contrast, many developing countries—and scholars who share their view— have historically argued that there is no such rule and that CIL allows substantial flexibility to the host state in determining appropriate compensation. See id. at 1083–86; Guzman, Andrew T., Why LDCs Sign Treaties That Hurt Them: Explaining the Popularity of Bilateral Investment Treaties, 38 Va. J. Int’l L. 639, 646–51 (1998)Google Scholar.

⁸⁹ see Guzman, supra note 88; Sornarajah, M., The International Law on Foreign Investment 435–88 (2d ed. 2004)CrossRefGoogle Scholar; Alvarez, José E., The Public International Law Regime Governing International Investment, 344 Recueil Des Cours 193, 292–95 (2009)Google Scholar.

⁹⁰ The possibility of such rules is well accepted in international case law. See, e.g., Asylum (Colom./Peru), 1950 ICJ Rep. 266 (Nov. 20); Right of Passage over Indian Territory (Port. v. India), 1960 ICJ Rep. 6 (Apr. 12); Mendelson, Maurice H., The Formation of Customary International Law, 272 Recueil Des Cours 155, 216 (1998)Google Scholar.

⁹¹ see Ohlin, Jens David, Nash Equilibrium and International Law, 23 Eur. J. Int’l L. 915, 936 (2012)CrossRefGoogle Scholar.

⁹² see Roberts, Sir Ivor, Satow’s Diplomatic Practice 128–30 (6th ed. 2009)CrossRefGoogle Scholar. On the frequency of traffic offenses by diplomats in the United Kingdom, see Denza, Eileen, Diplomatic Law 288–89 (3d ed. 2008)Google Scholar.

⁹³ See supra note 64 and accompanying text.

⁹⁴ see Dickinson, Laura,Military Lawyers on the Battlefield:An Empirical Account of International Law Compliance, 104 AJIL 1 (2010)CrossRefGoogle Scholar.

⁹⁵ See, e.g., White House Press Release, Remarks by the President at the National Defense University (May 23, 2013), at http://www.whitehouse.gov/the-press-office/2013/05/23/remarks-president-national-defense-university; John O. Brennan, The Ethics and Efficacy of the President’s Counterterrorism Strategy, Lawfare (Apr. 30, 2012), at http://www.lawfareblog.com/2012/04/brennanspeech/.

⁹⁶ Schmitt, Eric & Shanker, Thom, U.S. Weighed Use of Cyberattacks to Weaken Libya, N.Y. Times, Oct. 18, 2014, at A1 Google Scholar. Other examples from U.S. practice might include the State Department’s declaration, in determining to grant tax exempt status to property owned by foreign governments and used to house staff of permanent missions to the United Nations or the Organization of American States, that, “[a]s the largest foreign-government property owner overseas, the United States benefits financially much more than other countries from an international practice exempting staff residences from real property taxes, and it stands to lose the most if the practice is undermined.” Designation and Determination Under the Foreign Missions Act, 74 Fed. Reg. 31,788 (July 2, 2009). The exemption was expanded in January 2014 to cover additional property. see 79 Fed. Reg. 2927 (Jan. 16, 2014).

⁹⁷ Schmitt & Shanker, supra note 96.

⁹⁸ see IVTaft, William H. & Buchwald, Todd F., Preemption, Iraq and International Law, 97 AJIL 557 (2003)Google Scholar. It is worth noting that the Bush administration had articulated such a doctrine shortly before the war in the National Security Strategy of the United States of America 14–16 (2002),at http://www.state.gov/documents/organization/63562.pdf.

⁹⁹ To the extent that the NATO powers disclosed a legal rationale, they tried to circumscribe the precedential effect of their actions by articulating that rationale as narrowly as possible. The same approach was followed in the 2013 debates about potential military intervention in Syria. see Prime Minister’s Office, Chemical Weapon Use by Syrian Regime: UK Government Legal Position (Aug. 29, 2013), at https://www.gov.uk/government/publications/chemical-weapon-use-by-syrian-regime-uk-government-legal-position/chemical-weapon-use-by-syrian-regime-uk-government-legal-position-html-version.

¹⁰⁰ This concern also explains why states sometimes resist taking a position on CIL in the abstract, before they have had an opportunity to weigh the potential precedential impact of their statements.

¹⁰¹ see Fearon, James D., Bargaining, Enforcement, and International Cooperation, 52 Int’l Org. 269 (1998)CrossRefGoogle Scholar.

¹⁰² The prisoner’s dilemma is a game in the broader class of collaboration dilemmas.

¹⁰³ see Swaine, supra note 6, at 599 (“Customary international law... facilitates a choice not just between norms and anarchy, but also between norms in circumstances where states may be well disposed toward binding obligations.”)

¹⁰⁴ See supra note 79.

¹⁰⁵ see Michael P. Scharf, Customary International Law in Times of Fundamental Change: Recognizing Grotian Moments 107–22 (2013). Indeed, in several chapters of this book, Scharf emphasizes the role of the United States in articulating new CIL rules that subsequently gained widespread acceptance by other states.

¹⁰⁶ The court will also likely take a close look at states whose practice may be most important for Germany—such as its neighbors or major trade partners.

¹⁰⁷ For example, if the court finds that other states enter into bilateral treaties granting each other immunity, it might conclude that it would be best to require foreign states to enter into such a reciprocal treaty with Germany in order to receive that benefit, rather than applying it to all as a CIL rule.

¹⁰⁸ Thus, the early adopters of restrictive immunity, such as Belgium and Italy, supported their view of CIL— despite the lack of widespread state practice and opinio juris —by citing each other’s decisions, invoking fairness arguments, and arguing that a foreign state’s sovereignty and dignity are not compromised by holding it liable in respect of its commercial activities. see Harvard Research on International Law, Competence of Courts in Respect of Foreign States, 26 AJIL SUPP. 451, 613–14, 622–25 (1932). In a sense, they genuinely believed that their view of the CIL rule was the objective and correct one, and they were ultimately vindicated as other states followed their lead. Conversely, as late as the 1980s, Communist states like China and the Soviet Union actively resisted the ILC’s efforts to codify restrictive immunity. They argued that the ILC disregarded the practice and opinio juris of many states and that the new doctrine was incompatible with fundamental principles of international law such as sovereign equality and independence. See, e.g., Memorandum Presented by Mr. Nikolai A. Ushakov, Jurisdictional Immunities of States and Their Property, UN Doc. A/CN.4/371 (May 11, 1983), reprinted in [1983] 2 Y.B. Int’l L. Comm’n 53.

¹⁰⁹ see International Law Association, Committee on the Formation of Customary (General) International Law, Statement of Principles Applicable to the Formation of General Customary International Law 2, 4–5 (2000) (CIL formation rules themselves are determined by the practice of states); Mendelson, supra note 90.

¹¹⁰ Kelly, supra note 3, at 451.

¹¹¹ See, e.g., Crawford, supra note 83, at 23.

¹¹² See, e.g., Statute of the International Court of Justice, supra note 1, Art. 38(1)(b); Third Restatement, supra note 1, §102(2); S.S. “Lotus” (Fr.v.Turk.), 1927 PCIJ (Ser.A) No. 10, at 28(Sept. 7); North Sea Continental Shelf, supra note 56, para. 77; Continental Shelf (Libya/Malta), 1985 ICJ Rep. 13, para. 27 (June 3); Military and Paramilitary Activities in and Against Nicaragua, supra note 73, para. 183; Legality of the Threat or Use of Nuclear Weapons, Advisory Opinion, 1996 ICJ Rep. 226, para. 67 (July 8); Daillier, Patrick, Forteau, Mathias & Pellet, Alain, Droit International Public 353 (8th ed. 2009)Google Scholar; Shaw, Malcolm N., International Law 74–76 (6th ed. 2008)CrossRefGoogle Scholar; Hugh Thirlway, International Customary Law and Codification 46–47 (1972); Wolfke, Karol, Custom in Present International Law 40–41 (2d ed. 1993)Google Scholar.

¹¹³ On these debates, see Goldsmith & Posner, supra note 3, at 23–24; Guzman, supra note 2, at 185–86.

¹¹⁴ For example, in the case of state immunity, some states had low “thresholds” because they conducted relatively little state trading and placed a higher value on giving plaintiffs the ability to sue. These states insisted as early as the late nineteenth century that restrictive immunity was CIL, though they were a small minority at the time. Conversely, states that placed a high value on absolute immunity continued to insist it was CIL long after they themselves became the minority. The phenomenon is further complicated because, even for states that value the rule more or less equally, their evaluation might differ because they care about the practice of different foreign states. For example, even if France intrinsically valued restrictive immunity as much as Japan, it might switch much earlier because a larger proportion of its trade partners have already switched. Thus, although most observers would agree that the CIL rule shifted during that period, it is nearly impossible to elaborate rules to designate a single moment at which it shifted, as opposed to moments where individual states changed their views of the CIL rule. In addition, any rules that purported to identify with precision the moment when CIL rules change would not be followed consistently across different areas of CIL. This is because those states that have “low” thresholds in one area, such as immunity, and would therefore would insist on rules that allow CIL to change relatively easily may well have “high” thresholds in other areas, such as human rights, and therefore articulate more restrictive arguments in that context.

¹¹⁵ The dissent of Judge Read in the 1951 Fisheries case is sometimes read as such: “The only convincing evidence of State practice is to be found in seizures, where the coastal State asserts its sovereignty over the waters in question by arresting a foreign ship and by maintaining its position in the course of diplomatic negotiation and international arbitration.” Fisheries (UK v. Nor.), 1951 ICJ Rep. 116, 186, 191 (Dec. 18) (Read, J., dissenting). See also Anthony D’Amato, The Concept of Custom in International Law 50–51, 88 (1971). Wolfke has argued along similar lines, although he allows that in certain cases such as the Truman Proclamation, “the certainty that the verbal acts will be followed by deeds is nearly absolute and may, therefore, be considered not only as evidence but even, for simplification, as elements of custom-generating practice itself.” Wolfke, supra note 112, at 41–42.

¹¹⁶ Bellinger, John B. III, & Haynes, William J. II, A US Government Response to the International Committee of the Red Cross Study Customary International Humanitarian Law, 89 Int’l Rev. Red Cross 443, 445 (2007)Google Scholar.

¹¹⁷ see Dionisio Anzilotti, Cours De Droit International 74–75 (1929); Strupp, Karl, Les règles générales du droit de la paix, 47 Recueil Des Cours 263, 313–15 (1934 I)Google Scholar. These authorities are discussed in Mendelson, supra note 90, at 198.

¹¹⁸ Indeed, these writers seemed to contemplate that the only acts that should count are those of the specific officials capable of entering binding international agreements. see International Law Association, supra note 109, at 17.

¹¹⁹ This position is suggested by frequent reliance by courts and other CIL interpreters on national laws and other legal materials rather than on discrete instances of state practice. See, e.g., The Paquete Habana, 175 U.S. 677 (1900).

¹²⁰ see Third Restatement, supra note 1, §102 cmt. b; International Law Association, supra note 109, at 13–14; Shaw, supra note 112, at 83–84; Akehurst, supra note 87, at 2–3.

¹²¹ see Daillier Et Al., supra note 112, at 355–56; International Law Association, supra note 109, at 17–18; id. at 14 n.32 (list of cases); Shaw, supra note 112 at 82. The International Law Association may be incorrect, how ever, in suggesting that, as a general rule, the executive’s position should carry more weight if it conflicts with that of other branches. Our theory suggests the most relevant branch should be the one that effectively determines the state’s policy with respect to the issue in question.

¹²² see International Law Association, supra note 109, at 13–14; Shaw, supra note 112, at 84.

¹²³ see North Sea Continental Shelf, supra note 56, paras. 73–74; see also International Law Association, supra, at 20–26.

¹²⁴ See, e.g., Third Restatement, supra note 1, §102 cmt. b; International Law Association, supra note 109, at 25–26; Wolfke, supra note 112, at 43–44.

¹²⁵ Crawford, supra note 83, at 24; see also International Law Association, supra note 109, at 25.

¹²⁶ see International Law Association, supra note 109, at 20 n.47.

¹²⁷ see Third Restatement, supra note 1, §102 cmt. b; Crawford, supra note 83, at 25; International Law Association, supra note 109, at 23.

¹²⁸ see Fisheries (UK v. Nor.), supra note 115, at 131, 138; North Sea Continental Shelf, supra note 56, paras. 73–74; Military and Paramilitary Activities in and Against Nicaragua, supra note 73, para. 186; Asylum, supra note 90, 276–77; Crawford, supra note 83, at 24.

¹²⁹ see North Sea Continental Shelf, supra note 56, para. 74; Third Restatement, supra note 1, §102 cmt. b; Crawford, supra note 83, at 24; International Law Association, supra note 109, at 20; Shaw, supra note 112, at 76. Frequently cited examples of CIL rules that emerged overa short period include sovereignty over airspace and coastal state rights over the continental shelf. See, e.g., Third Restatement, supra note 1, §102 Reporters Note 2.

¹³⁰ see North Sea Continental Shelf, supra note 56, para. 74; Charles De Visscher, Theory and Reality in Public International Law 155 (P. E. Corbett trans., 1968); Guzman, supra note 2, at 189; International Law Association, supra note 109, at 26; Shaw, supra note 112, at 79–80; Wolfke, supra note 112, at 78–79; René-Jean Dupuy, Coutume sage et coutume sauvage, in Mélanges Offerts à Charles Rousseau 75, 77–78 (1974).

¹³¹ As Thirlway put it:

Thirlway, supra note 112, at 47.

¹³² Third Restatement, supra note 1, §102(2).

¹³³ For the former view, see, for example, G. I. Tunkin, Theory of International Law 123–24 (William E. Butler trans., 1974), I. C. MacGibbon, Customary International Law and Acquiescence, 1957 Brit. Y.B. Int’l L. 115, and Strupp, supra note 117, at 263. For the latter, see Hans Kelsen, Principles of International Law 311–17 (1952), and Thirlway, supra note 112, at 59.

¹³⁴ See, e.g., Daillier, Forteau & Pellet, supra note 112, at 354–55; International Law Association, supra note 109 at 31, 38–40; Shaw, supra note 112, at 75.

¹³⁵ see International Law Association, supra note 109, at 33; Wolfke, supra note 112, at 47.

¹³⁶ see Third Restatement, supra note 1, §102 Reporters Note 2; D’Amato, supra note 115; International Law Association, supra note 109, at 33; Shaw, supra note 112, at 86–87; Thirlway, supra note 112, at 47; Wolfke, supra note 112, at 47.

¹³⁷ The classical statement is in North Sea Continental Shelf, supra note 56, para. 77. See also Continental Shelf (Libya/Malta), supra note 112, para. 27; Military and Paramilitary Activities in and Against Nicaragua, supra note 73, para. 207; Legality of the Threat of Use of Nuclear Weapons, supra note 112, para. 67; S.S. “Lotus,” supra note 112, at 28.

¹³⁸ This view is often buttressed by references to ICJ and Permanent Court of International Justice decisions in which the court appeared not to require separate evidence of opinio juris when it believed state practice to be sufficiently clear. See, e.g., Barcelona Traction, Light & Power Co. (Belg. v. Spain), 1970 ICJ Rep. 3, para. 70 (Feb. 5); Fisheries (UK v. Nor.), supra note 115, at 128; Interhandel (Switz. v. U.S.), 1959 ICJ Rep. 6, 27 (March 21); Nottebohm (Liech. v. Guat.), 1944 ICJ Rep. 4, 22 (Apr. 6); S.S. “Wimbledon” (UK v. Ger.), 1923 PCIJ (Ser. A) No. 1, at 25 (Aug. 17). Indeed, as Crawford, supra note 83, at 26, observes, “The International Court will often infer the existence ofopinio iuris from ageneral practice, from scholarly consensus or from its own or other tribunals’ previous determinations.” See also Sir Hersch Lauterpacht, The Development of International Law by the International Court 380 (1958); Wolfke, supra note 112, at 44. In its 2000 statement of principles, the International Law Association went beyond this fairly conventional position by arguing that opinio juris is not necessary at all in normal circumstances: a CIL rule may be inferred directly from sufficient practice except in relatively infrequent circumstances in which some evidence suggests that states believe that the practice does not give rise to a legal right or obligation. International Law Association, supra note 109, at 29–38. The ILA’s position is controversial, however, and has not been generally accepted. see Wood, supra note 2, at 305.

¹³⁹ see Paul Guggenheim, Les deux éléments de la coutume en droit international, in La technique et les principes du droit international public. Etudes en l’honneur de Georges Scelle 275 (1950); Kelsen, Hans, Théeorie du droit international coutumier, 1 Revue internationale de la théorie du droit 253, 263–67 (1939)Google Scholar; Kopelmans, Lazare, Custom As a Means of the Creation of International Law, 1937 Brit. Y.B. Int’l L. 127, 151Google Scholar.

¹⁴⁰ See, e.g., Cheng, Bin, United Nations Resolutions on Outer Space: “Instant” International Customary Law?, 5 Indian J. Int’l L. 23 (1965)Google Scholar; Guzman, supra note 2, at 200–01, 204; International Law Association, supra note 109, at 41–42.

¹⁴¹ see Dupuy, supra note 130; Kirgis, Frederic L. Jr., Custom on a Sliding Scale, 81 AJIL 146 (1987)CrossRefGoogle Scholar; Roberts, Anthea Elizabeth, Traditional and Modern Approaches to Customary International Law: A Reconciliation, 95 AJIL 757 (2001)CrossRefGoogle Scholar; Schachter, Oscar, Entangled Treaty and Custom, in International Law at a Time of Perplexity: Essays in Honour of Shabtai Rosenne 717, 731 (>Yoram Dinstein ed., 1989)Google Scholar.

¹⁴² The same fundamental idea is expressed in Mendelson, supra note 90, at 188.

¹⁴³ This understanding is consistent with modern doctrineto the effect that what matters are objectively verifiable claims or statements, rather than some inquiry into the subjective beliefs of actors. See, e.g., International Law Association, supra note 109, at 33; Thirlway, supra note 112, at 54; Wolfke, supra note 112, at 47; Cheng, supra note 140, at 36; Norman & Trachtman, supra note 6, at 570; Swaine, supra note 6, at 615; Virally, Michel, Sources of International Law, in Manual of Public International Law 116, 134 (Sørensen, Max ed., 1968)Google Scholar.

¹⁴⁴ see Akehurst, supra note 87, at 3.

¹⁴⁵ See, for example, the ICJ cases cited supra note 138.

¹⁴⁶ see Kelly, supra note 3, at 487; Reisman, supra note 3, at 137.

¹⁴⁷ Military and Paramilitary Activities in and Against Nicaragua, supra note 73, para. 186. See also the International Committee of the Red Cross’s views in Henckaerts, Jean-Marie, Study on Customary International Humanitarian Law: A Contribution to the Understanding and Respect for the Rule of Law in Armed Conflict, 87 Int’l Rev. Red Cross 175, 180 (2005)CrossRefGoogle Scholar.

¹⁴⁸ see Guzman, supra note 2, at 200–01; Cheng, supra note 140.

¹⁴⁹ See, e.g., Texaco Overseas Petroleum Co.v. Libyan Arab Republic 17 ILM 1(1978) (Dupuy, sole arb., 1977) (finding that UN resolutions on the legality of expropriation passed by a large majority did not reflect CIL because that majority was not sufficiently representative, and that an earlier resolution more consistent with preexisting practice and opinio juris remained the more accurate statement of CIL); Legality of the Threat of Use of Nuclear Weapons, supra note 112, para. 71 (finding that repeated UN resolutions declaring the use of nuclear weapons to be illegal “fall short of establishing the existence of an opinio juris on the illegality of the use of such weapons”). But see Military and Paramilitary Activities in and Against Nicaragua, supra note 73, paras. 188–91 (relying on UN General Assembly resolutions to support its finding that the UN Charter principles regarding the use of force are CIL); International Law Association, supra note 109, at 57–59 (proposing that some General Assembly resolutions may be rebuttable evidence of CIL, but under strict conditions).

¹⁵⁰ see International Law Association, supra note 109.

¹⁵¹ see Guzman, supra note 2, at 201–04.

¹⁵² Roberts, Anthea, Comparative International Law: The Role of National Courts in Creating and Enforcing International Law, 60 Int’l & Comp. L.Q. 57(2011)CrossRefGoogle Scholar, emphasizes the dual role of domestic courtsin applying CIL (and International Law in general); in addition to being impartial interpreters of the law, they are national institutions that legitimately try to shape International Law consistent with their states’ interests. See also Stephan, Paul B., Disaggregating Customary International Law, 21 Duke J. Comp. & Int’l L. 191, 198 (2010)Google Scholar.

¹⁵³ see International Law Association, supra note 109, at 18–19; Dinstein, supra note 74, at 317.

¹⁵⁴ see Statute of the International Court of Justice, supra note 1, Art. 59; Certain German Interests in Polish Upper Silesia (Ger. v. Pol.), 1926 PCIJ (Ser. A) No.7, at 19 (May 25); Crawford, supra note 83, at 37–39.

¹⁵⁵ see Statute of the International Court of Justice, supra note 1, Art. 38(1)(d); Third Restatement, supra note 1, §103.

¹⁵⁶ see International Law Association, supra note 109, at 18–19.

¹⁵⁷ Higgins, supra note 73, at 202;see also Third Restatement,supra note 1,§103cmt.b; Shaw,supra note 112, at 109; Ginsburg, Tom, Bounded Discretion in International Judicial Lawmaking, 45 Va. J. Int’l L. 631, 639 (2005)Google Scholar (“In practice,... customary law is often first identified by courts.”).

¹⁵⁸ See, e.g., Katzenstein, Suzanne, International Adjudication and Custom Breaking by Domestic Courts, 62 Duke L.J. 671 (2012)Google Scholar; see also Benvenisti, Eyal & Downs, George W., National Courts, Domestic Democracy, and the Evolution of International Law, 20 Eur. J. Int’l L. 59, 63 (2009)CrossRefGoogle Scholar (“[International adjudicatory bodies] are in a position to act as agenda setters by having an early opportunity to interpret international norms, and thus establish a legal focal point which can function to narrow the range of options that remain open to national legislatures and courts.”)

¹⁵⁹ see Huth, Paul K., Croco, Sarah E. & Appel, Benjamin J., Bringing Law to the Table: Legal Claims, Focal Points, and the Settlement of Territorial Disputes Since 1945, 57 Am. J. Pol. Sci. 90 (2013)CrossRefGoogle Scholar; Johns, Leslie, Courts as Coor dinators: Endogenous Enforcement and Jurisdiction in International Adjudication, 56 J. Conflict Resol. 257 (2012)CrossRefGoogle Scholar.

¹⁶⁰ see Alvarez-Jiménez, Alberto, Methods for the Identification of Customary International Law in the International Court of Justice’s Jurisprudence: 2000–2009, 60 Int’l & Comp. L.Q. 681, 705 (2011)CrossRefGoogle Scholar.

¹⁶¹ see Ginsburg, supra note 157, at 640.

¹⁶² This effect will be stronger if the decision comes from a court that has more legal and institutional ability to impose its decisions within the relevant national legal system. For instance, from the perspective of a third state, a decision of the European Court of Justice or the European Court of Human Rights adopting a CIL rule significantly increases the likelihood that the states subject to their respective jurisdiction will uphold the rule in the future.

¹⁶³ International court decisions may also affect state behavior through other channels. For example, Helfer and Slaughter argue that they can mobilize domestic constituencies that press their governments for compliance with international law. see Helfer, Laurence R. & Slaughter, Anne-Marie, Why States Create International Tribunals: A Response to Professors Posner and Yoo, 93 Cal. L. Rev. 899, 935–36 (2005)Google Scholar.

¹⁶⁴ see Higgins, supra note 73, at 202; Roberts, supra note 152, at 90–91.

¹⁶⁵ Supra note 138.

¹⁶⁶ see Wolfke, supra note 112, at 72–76; Alvarez-Jiménez, supra note 160, at 689–93; Charney, Jonathan I., Universal International Law, 87 AJIL 529, 537 (1993)CrossRefGoogle Scholar.

¹⁶⁷ Jurisdictional Immunities of the State (Ger. v. It.; Greece intervening) (Int’l Ct. Justice Feb. 3, 2012). In several other case the ICJ has followed a conservative path. see Ahmadou Sadio Diallo (Guinea v. Dem. Rep. Congo), Preliminary Objections, 2007 ICJ Rep. 582, paras. 89–94 (May 24) (declining to find that CIL allows states to exercise diplomatic protection by substitution); Arrest Warrant of 11 April 2000 (Dem. Rep. Congov. Belg.), 2002 ICJ Rep. 3 (Feb. 14) (refusing to recognize universal jurisdiction for grave violations of international humanitarian law and exceptions to head of state immunity despite some national court decisions to the contrary); Legality of the Threat of Use of Nuclear Weapons, supra note 112 (declining to find a CIL rule prohibiting the threat or use of nuclear weapons); North Sea Continental Shelf, supra note 56 (declining to find that the equidistance rule for continental shelf delimitation has become CIL).

¹⁶⁸ see Katzenstein, supra note 158. Katzenstein’s argument that this phenomenon is normatively undesirable appears to assume that the potential new rule is an improvement. But if, in fact, the defection is opportunistic and risks triggering the unraveling of a welfare-enhancing cooperative rule, it may be desirable for an international court to step in and reaffirm that rule. After all, states presumably created international courts so that they could play this function of affirming and enforcing existing law.

¹⁶⁹ Indeed, scholars have argued that by considering an issue area to be governed by CIL, states may sometimes be intentionally delegating to international courts the authority to develop appropriate rules. see Benvenisti, supra note 14; Robert E. Scott & Paul B. Stephan, The Limits of Leviathan 34–35 (2006).

¹⁷⁰ Although we believe the mechanism by which international court decisions may influence CIL should apply to courts beyond the ICJ, there may be important differences in their approaches to CIL and in the objectives they pursue. See, e.g., Neuman, Gerald L., Import, Export and Regional Consent in the Inter-American Court of Human Rights, 19 Eur. J. Int’l L. 101 (2008)CrossRefGoogle Scholar. In some circumstances, international courts may compete to shape CIL, leading to fragmentation. A full exploration of this phenomenon is beyond the scope of this article.

¹⁷¹ Vienna Convention on the Law of Treaties, supra note 55, Art. 34.

¹⁷² Id., Art. 38. The ILC commentary adds: “The role played by custom in sometimes extending the application of rules contained in a treaty beyond the contracting States is well recognized.” Reports of the Commission to the General Assembly, pt. 1, Report of the International Law Commission on the Work of the Second Part of Its Seventeenth Session, UN Doc. A/6309/Rev.1, reprinted in [1966] 2 Y.B. Int’l L. Comm’n 169, 230, UN Doc.A/CN.4/SER.A/1966/Add.1.

¹⁷³ Third Restatement, supra note 1, §102(3).

¹⁷⁴ See, e.g., North Sea Continental Shelf, supra note 56, para. 70; see also Continental Shelf (Libya/Malta), supra note 112, para. 27; Military and Paramilitary Activities in and Against Nicaragua, supra note 73, para. 188.

¹⁷⁵ See, e.g., Crawford, supra note 83, at 31–32; Shaw, supra note 112, at 95–98; Villiger, Mark E., Customary International Law and Treaties 173–75 (2d ed. 1997)Google Scholar; Baxter, R. R., Treaties and Custom, 129 Recueil Des Cours 25 (1970 I)Google Scholar; Robert Y. Jennings, Law-Making and Package Deal, in Le droit international: Unité et diversité. MéLanges offerts à Paul Reuter 347 (1981).

¹⁷⁶ see North Sea Continental Shelf, supra note 56, paras. 75–77; Villiger, supra note 175, at 182; Dinstein, supra note 74, at 376.

¹⁷⁷ The parties may have intended to establish legal obligations among themselves when there were none, or even to contract out of a CIL rule, in which case the act of signing or ratifying the treaty is inconsistent with a parallel CIL rule. Or they may have intended to codify, clarify, or provide institutional mechanisms to sustain a CIL rule, in which case the act is consistent with such a rule. See, e.g., Ahmadou Sadio Diallo, supra note 167, at 615; Villiger, supra note 175, at 27–28. Likewise, failure to ratify is ambiguous: it may express disagreement with the rule but may also result from many other motivations. see Baxter, supra note 175, at 66–67.

¹⁷⁸ see North Sea Continental Shelf, supra note 56, para. 76; Villiger, supra note 175, at 183.

¹⁷⁹ see Baxter, supra note 175, at 64.

¹⁸⁰ See, e.g., Schachter, supra note 141, at 729.

¹⁸¹ see Dinstein, supra note 74, at 377; Villiger, supra note 175, at 183–84.

¹⁸² see North Sea Continental Shelf, supra note 56, paras. 76–78. In the case of widely ratified treaties, reliance on the practice of nonparties is even more problematic since they may constitute only a small and unrepresentative minority.

¹⁸³ see North Sea Continental Shelf, supra note 56, paras. 77–78.

¹⁸⁴ see Baxter, supra note 175, at 64; Dinstein, supra note 74, at 378. The Nicaragua case was an extreme example of this problem, as virtually all states are parties to the UN Charter.

¹⁸⁵ North Sea Continental Shelf, supra note 56, para. 72. For criticism, see, for example, Baxter, supra note 175, at 62–64, and Dinstein, supra note 74, at 363–65.

¹⁸⁶ see Baxter, supra note 175, at 38 (“[T]he very fact that the parties acknowledge rules to be rules of customary International Law indicates their willingness to apply those rules in relations not governed in strict law by the terms of the treaty.”).

¹⁸⁷ See, e.g., UN Convention on the Law of the Sea, supra note 87, Art. 137 (providing that “No State shall claim or exercise sovereignty or sovereign rights over any part of [the seabed and ocean floor and subsoil thereof] or its resources... .”). See generally Dinstein, supra note 74, at 332–33.

¹⁸⁸ see Baxter, supra note 175, at 42; Dinstein, supra note 74, at 361–62. But often it is unclear whether the provisions of a treaty purport to codify CIL or to develop it. Even the ILC does not consistently adhere to the distinction between “codification” and “progressive development” in its statute. see Villiger, supra note 175, at 187; Baxter, supra, at 41.

¹⁸⁹ Baxter, supra note 175, at 55.

¹⁹⁰ For example, they might disagree with other substantive or procedural provisions of the treaty.

¹⁹¹ see Dinstein, supra note 74, at 378–79; Villiger, supra note 175, at 187.

¹⁹² Thus, the Third Restatement states that a “wide network of similar bilateral arrangements on a subject may constitute practice and also result in customary law.” Third Restatement, supra note 1, §102 cmt. i.

¹⁹³ see Villiger, supra note 175, at 189; Dinstein, supra note 74, at 348, 375–76; Schachter, supra note 141, at 732.

¹⁹⁴ see International Law Association, supra note 109, at 47–48; Charney, Jonathan I., International Agreements and the Development of Customary International Law, 61 Wash. L. Rev. 971, 980 (1986)Google Scholar. A fortiori, treaties entered into to settle specific issues between states (rather than establish rules generally applicable to their relations) do not give rise to CIL. see International Law Association, supra, at 45.

¹⁹⁵ see Charney, supra note 194, at 983; see also Baxter1, R. R., Multilateral Treaties as Evidence of Customary International Law, 1966 Brit. Y.B. Int’l L. 275, 284Google Scholar; Schachter, supra note 141, at 735.

¹⁹⁶ see Crawford, supra note 83, at 31 (“Law-making treaties create general norms, framed as legal propositions, to govern the conduct of the parties, not necessarily limited to their conduct inter se —indeed the expression of an obligation in universal or ‘all states’ form is an indication of an intent to create such a general rule.”) Some authors have suggested that such rules are more likely to give rise to CIL when the treaties focus on human rights obligations or other “generalized interests and aspirations of the international community.” Charney supra note 194, at 981–83.

¹⁹⁷ see Third Restatement, supra note 1, pt. V, Introductory Note; id., §511, Reporters Note 8; id., §514 cmt. a; Continental Shelf (Libya/Malta), supra note 112, at 29–34 (recognizing the EEZ as CIL); Delimitation of the Maritime Boundary in the Gulf of Maine Area (Can./U.S.), 1984 ICJ Rep. 246, paras. 94–96 (Oct. 12) (recognizing certain aspects of the continental shelf and EEZ as CIL).

¹⁹⁸ For now, we bracket the question of whether and how other states benefit from another state’s compliance with such obligations. Our point is simply that, to the extent such benefits exist, non parties to the treaty cannot be excluded from them.

¹⁹⁹ The same can be said of treaties that purport to create or codify general rules that are not bargain-like but that have a coordinating function, such as the Vienna Convention on the Law of Treaties’ interpretation provisions. Indeed, such provisions are frequently recognized as CIL by international courts and tribunals. see Dinstein, supra note 74, at 353.

²⁰⁰ By contrast, treaties that try to set universal nonderogable rules (for example, the Torture Convention) may function more like CIL: states may comply to avoid undermining the norm (making the treatya “dead letter”) rather than because of threats of reciprocity or retaliation. This interpretation is consistent with the absence in such treaties of features commonly found in other treaties to facilitate reciprocity, such as flexibility and countermeasures provisions.

²⁰¹ North Sea Continental Shelf, supra note 56, para. 72.

²⁰² see International Law Association,supra note 109, at 52–53; Villiger,supra note 175, at 177 (“General rules may be defined as intending to regulate pro futuro, with regard to a potentially unlimited, general number of subjects, rather than individualized ones.”), 178 (“[S]ince customary law is usually general, a smooth transition from the conventional to the identical customary rule requires that the conventional rule also be general.”)

²⁰³ North Sea Continental Shelf, supra note 56, para. 72. On reservations contradicting the CIL status of a treaty provision, see Baxter, supra note 195, at 284. But see International Law Association, supra note 109, at 44–45.

²⁰⁴ See supra note 185.

²⁰⁵ Convention Against Torture and Other Cruel, Inhuman or Degrading Treatment or Punishment, Dec. 10, 1984, 1465 UNTS 85.

²⁰⁶ Thus, the ICJ also emphasized that, as with other CIL rules, time and consistency of practice were relevant when a treaty provision is alleged to give rise to CIL. see North Sea Continental Shelf, supra note 56, paras. 73–74; see also International Law Association, supra note 109, at 53–54. The court also held that “this result is not lightly to be regarded as having been attained.” North Sea Continental Shelf, supra, para. 71. Consistent with our theory, scholars have recognized that the practice of parties toward nonparties may be especially probative of a CIL rule. see International Law Association, supra note 109, at 47.

²⁰⁷ The similarities are especially strong when states adopt domestic legislation that clearly binds domestic courts (and other legal actors) to apply the treaty obligation. see Dinstein, supra note 74, at 379.

²⁰⁸ Even among the parties, a consequence of using most-favored-nation clauses in BITs is that states may in some circumstances avail themselves of concessions made to others, thus weakening the strictly reciprocal nature of the bargain. see Schill, Stephan W., Multilateralizing Investment Treaties Through Most-Favored-Nation Clauses, 27 Berkeley J. Int’l L. 496 (2009)Google Scholar.

²⁰⁹ see Alvarez, José E., A BIT on Custom, 42 N.Y.U.J. Int’l L. & Pol. 17, 31 (2009)Google Scholar. Note, though, that in line with the discussion of opinio juris above, BIT provisions that “explicitly or implicitly rely on general international law or reflect an intent by their drafters to affirm traditional principles of state responsibility to aliens” are more likely to support CIL rules. Id. at 31–34.

²¹⁰ See, e.g., North Sea Continental Shelf, supra note 56, para. 60.

²¹¹ see Third Restatement, supra note 1, §102 cmt. d & Reporters Note 2; International Law Association, supra note 109, at 27. Many leading scholars also recognize the exception. See, e.g., Crawford, supra note 83, at 28; Daillier et al., supra note 112, at 363; Charles Rousseau, 1 Droit International public: introduction et Sources 320, 326 (1970); Thirlway, supra note 112, at 109–10; Wolfke, supra note 112, at 66–67; Akehurst, supra note 87; Mendelson, supra note 90, at 227–44. As discussed below, the persistent objector doctrine is also alluded to in some international court decisions, although their significance is debated.

²¹² For a classic exposition of this argument, see Weil, Prosper, Towards Relative Normativity in International Law, 77 AJIL 413, 433–34 (1983)CrossRefGoogle Scholar.

²¹³ see Charney, supra note 73; Dumberry, Patrick, Incoherent and Ineffective: The Concept of Persistent Objector Revisited, 59 Int’l & Comp. L.Q. 779 (2010)CrossRefGoogle Scholar; Stein, supra note 85.

²¹⁴ Fisheries (UK v. Nor.), supra note 115, at 131. Likewise, in the Domingues case, the Inter-American Commission on Human Rights found that the prohibition on imposing the death penalty on minors was jus cogens, with the consequence that the persistent objector doctrine was inapplicable. Domingues v. United States, Case 12.285, Inter-Am. Comm’n H.R., Report No. 62/02 (2002). For critical discussion of the cases invoked in support of the persistent objector doctrine, see Charney, supra note 73, at 9–11, and Dumberry, supra note 213, at 784–90. But see Mendelson, supra note 90, at 228–33.

²¹⁵ The Third Restatement admits as much. see Third Restatement, supra note 1, §102 cmt d; see also Charney, supra note 73, at 11–16; Dumberry, supra note 213, at 791–94; Stein, supra note 85, at 459–63.

²¹⁶ Dem. Rep. Congo v. FG Hemisphere Assocs., [2011] 14 HKCFAR 95, para. 44 (CFA), available at http://legalref.judiciary.gov.hk/lrs/common/.

²¹⁷ see Crawford, supra note 83, at 28 n.45.

²¹⁸ Thus, in cases brought against China, U.S. courts apply the commercial exception as they do against other states. See, e.g., CYBERsitter, LLC v. China, 805 F.Supp.2d 958 (C.D. Cal. 2011) (finding jurisdiction in suit against China for misappropriation of trade secrets, copyright infringement, unfair competition, and civil conspiracy in connection with a commercial activity).

²¹⁹ UN Convention on Jurisdictional Immunities of States and Their Property, GA Res. 59/38, annex (Dec. 2, 2004).

²²⁰ See supra notes 83–87 and accompanying text.

²²¹ see Fisheries Jurisdiction (UK v. Ice.), supra note 83.

²²² see Charney, supra note 73, at 10–11.

²²³ There are special circumstances in which the persistent objector doctrine might appear more significant, but upon closer examination its role remains marginal. First, the objecting states may be successful in preventing others from applying the new rule. For instance, if the U.S., UK, and Japanese navies had consistently and successfully defended their states’ fishing vessels within the purported exclusive zones of other states, they would have effectively prevented the new rule from being applied against them. This kind of enforcement, however, is likely to be very costly and infrequent. Also, most international lawyers would not characterize such an outcome as an application of the persistent objector doctrine but as one in which states successfully prevented the purported new CIL rule from emerging at all. Second, in some cases—such as for most human rights CIL norms—other states may not have the ability to withhold the benefit of the “old” rule from the persistent objector. For example, suppose that a general CIL rule prohibiting the death penalty were to be widely accepted. A state that persistently objected could continue applying the death penalty within its own territory, invoking its persistent objector status. Other states could not prevent it from doing so except at great cost, which may give the impression that the state indeed benefits from an exception to the rule because of its objector status. However, other states could denounce the objector’s actions, complain before international tribunals and review mechanisms, and perhaps even try its officials in their own courts. If acceptance of the new rule was sufficiently widespread, they could argue that it had attained jus cogens status, thus defeating the persistent objector doctrine. In such a case, even though the violation might continue indefinitely, the consequences for the objector would not be much different from those that attach to violation of a human rights CIL norm in the absence of the persistent objector doctrine. Thus, it is unclear that the objector would derive any real benefit from invoking the doctrine.

²²⁴ Goldsmith & Posner, supra note 3, at 45–54.

²²⁵ Id. at 54.

²²⁶ More precisely, on one side of scale are the short-term benefits of defecting; on the other, the costs, including precedential concerns and also any expected costs of retaliation and reputational loss.

²²⁷ see Goldsmith & Posner, supra note 3, at 46.

²²⁸ The fact that these two sets of circumstances are often present at the same time is not coincidental. When states expect to face situations in which the ability to make case-by-case decisions and enforce CIL rules through reciprocity and retaliation is valuable, they will tend to entrust these decisions to institutions capable of doing so.

²²⁹ Our claims with regard to retaliation are modest. States do on occasion retaliate against violations of CIL norms, just as they retaliate against other actions that they wish to punish or deter. Yet, as seen above, the status of a norm as CIL does not necessarily make retaliation more likely, nor does CIL mitigate some of the undesirable effects of retaliation, such as the risk of escalation. Thus, although we believe that for most CIL rules, cooperation is unlikely to be sustained solely by retaliation, the use of retaliation and its playing a greater role for some CIL rules than for others do not undermine our account.

²³⁰ See supra notes 63–64; Stephan, supra note 152, at 201–02.

²³¹ see Third Restatement, supra note 1, §102 cmt. k.

²³² Indeed, it is widely seen as jus cogens. One of the implications is that, outside of self-defense, force may not be used as a countermeasure against a breach of international law. ILC Articles on State Responsibility, supra note 40, Art. 50(1)(a).

²³³ see Beth A. Simmons, Mobilizing for Human Rights(2009);see also Goldsmith & Posner,supra note 3, at 669 (“absent special circumstances..., a nation otherwise inclined to abuse its citizens gains nothing from declining to do so in return for a reciprocal commitment from another nation to do the same.”); Guzman, supra note 2, at 45.

²³⁴ Guzman, supra note 2, at 110–11.

²³⁵ See, e.g., Barcelona Traction, Light & Power Co., supra note 138, para. 34 (stating that “the principles and rules concerning the basic rights of the human person, including protection from slavery and racial discrimination” give rise to erga omnes obligations); Reservations to the Convention on the Prevention and Punishment of the Crime of Genocide, Advisory Opinion, 1951 ICJ Rep. 15,23(May 28) (recognizing the customary and universal character of the principles underlying the Genocide Convention).

²³⁶ see ILC Articles on State Responsibility, supra note 40, Art. 50(1)(b).

²³⁷ see Goldsmith & Posner, supra note 3, at 668–71.

²³⁸ Alan Dershowitz, Should Mohammed Be Tortured for Information?, at http://www.alandershowitz.com/publications/docs/mohammedtorture.html. Dershowitz is an advocate of limited uses of torture but consistently treats the precedent-setting effect as a serious and valid objection.

²³⁹ Indeed, the system facilitates this practice. see Hafner-Burton, Emilie, Helfer, Laurence & Fariss, Christopher, Emergency and Escape: Explaining Derogation from Human Rights Treaties, 65 Int’l Org. 673 (2011)CrossRefGoogle Scholar.

²⁴⁰ The term is from Emilie Hafner-Burton, Making Human Rights a Reality (2013).

²⁴¹ Jeffrey L. Dunoff & Mark A. Pollack, International Law and International Relations: Introducing an Interdis ciplinary Dialogue, in Interdisciplinary Perspectives on International Law and International Relations, supra note 12, at 3, 10.

²⁴² Raustiala, Kal, Form and Substance in International Agreements, 99 AJIL 581, 587 (2005)CrossRefGoogle Scholar.

²⁴³ For salient constructivist accounts of international law, see Jutta Brunnée & Stephen J. Toope, Legitimacy and Legality in International Law (2010); Goodman, Ryan & Jinks, Derek, How to Influence States: Socialization and International Human Rights Law, 54 Duke L.J. 621 (2005)Google Scholar.