The State Department of the United States of America has recognised that a number of rules set forth in the International Committee of the Red Cross (ICRC) Study on Customary International Humanitarian Law have achieved customary international law status. Nevertheless, the United States expressed doubts about the methodology used to determine that certain rules, argued to be insufficiently grounded in fact and evidence, and that lead to the country’s rejection of the Study. Specifically, the United States expressed concern in relation to the customary status of the Geneva Conventions and Protocols, and questioned that customary humanitarian law can be applied to both international and non-international armed conflicts.
In the view of the United States, the Study incorrectly declared rules to have customary law status, since the State practice analysed is insufficiently dense to meet the ‘extensive and virtually uniform’ standard required. In their opinion, the Study placed too much emphasis on materials, such as military manuals and other published guidelines, and also extensively relies on non-binding and ‘consensus-based’ resolutions of the General Assembly and other international actors. All in all, the United States affirmed that the Study does not pay due regard to the practice of ‘specially affected’ States, tending to regard as equivalent the practice of States without distinction of history, experience, and ‘greater quantity and quality of practice’. Furthermore, the US is critical of the opinio juris being analysed together with practice, as an act that reflects ‘both practice and legal conviction’, and not demonstrating ‘separately’ the existence of opinio juris. Specifically, the US found debatable the rules for the protection of humanitarian relief personnel, the damages prohibitions, and right to establish universal jurisdiction.
It is commonly observed that Article 38 of the Statute of the International Court of Justice (ICJ) contains the injunction that the Court determines customary law based on “evidence of a general practice accepted as law”. Practice by itself is not evidence of the existence of custom, and thus the norm must be “accepted as law”.
According to the jurisprudence of the ICJ new norms require both practice and opinio juris before they can be regarded as representing customary international law. In the North Sea Continental Shelf case, the ICJ also considered the ‘psychological’ requirement of opinio juris to include “the consciousness of conforming to a rule, that if the acts of practice are to be attributed to a motive other than such consciousness, they cannot show opinio juris”. Since the opinio juris is a state of mind, it is problematic to ascertain in the case of a State. However, opinio juris can be deduced from the State’s pronouncements and actions that are taken through its officials, in particular those actions to constitute the ‘practice’ element of customary international law. In consequence, State practice and opinio juris are to be set together, not separately. In the Nicaragua case, the Court declared not to consider that, for a rule to be established as customary law, the corresponding practice must be in absolute rigorous conformity with the rule. The Court deemed as sufficient that the conduct of States should in general be consistent with such rules, and that instances of State conduct inconsistent with a given rule should generally be treated as breaches of that rule, not as indications of the recognition of a new rule. Similarly, the ICJ decided in North Sea case that treaty provisions have passed into acceptance of opinio juris and thus are binding to all States, even those which have never become parties to the Convention. A process that is defined as ‘perfectly possible’, and “even without the passage of any considerable period of time”.
It is in principle possible for a State not to accept a rule which is in the process of becoming standard international practice. In clear and coherent opposition States are able to exempt themselves from the rule in formation when it does become rule of law. This is generally called ‘persistent objector’ status. Thus, the problem of the persistent objector remains open alongside rules of special customary law. Special customary law is a customary norm that only applies between a limited number of States, as the ICJ found in the Right of Passage over Indian Territory case. One relevant instance of the persistent objector was identified in the reasoning of the Asylum case. Peru had the status of persistent objector. This same notion identified in the former case is traced back to the Fisheries case between the United Kingdom and Norway, where the ICJ defined persistent objection as “always opposed to any attempt to apply it to their jurisdiction”. If a single State does not claim to be a persistent objector, and entitled to rely on rules different from those generally in force, such a claim could only be maintained as the result of a general clear coherent action by that State.
The suggestion of the United States as a persistent objector by reason of its objection to the norms identified by the ICRC Study, and therefore not necessarily bound by such rules, can neither rest on the assertion of a special custom nor a persistent objection.
The ICRC Study was initiated in December 1995, by the 26th International Conference of the Red Cross, with the purpose of providing uniform regulations for armed conflict. The first volume of the Study is divided into five parts. The first part contains a discussion of the principles of distinction and proportionality. The second part is a declaration of the protected persons and objects. The third part discusses permitted and prohibited methods of warfare. The fourth part relates to the use of weapons, and the last part concerns the treatment of civilians and personnes hors de combat. There is a section on Implementation that concludes the volume and concerns compliance, enforcement, responsibility and reparation. The second volume is divided into two parts, and gathers the evidence and sources for the previous part. It includes treaties and other relevant instruments, military manuals, legislation, case-law, practice of international organizations and international judicial bodies, together with the practice of the ICRC.
The Study sets out that rules, and the limits they impose, should be equally applicable in international and non-international armed conflicts by providing extensive evidence of the application of customary international rules in these contexts. In the view of the ICRC, States assumed this premise in 1949 with the adoption of common Article 3 of the Geneva Contentions, which was recognized through subsequent State practice in both international and non-international armed conflicts.
The Study defines as State practice the “physical and verbal acts of States”. It considers that the combined effect of what States say and what they actually do to be regarded as ‘operational practice’. The Study sets out that national legislation is State practice, which is relevant in the formation of international customary law. Evidence of customary law can be obtained from numerous sources, including administrative acts, legislations, court’s decisions, and activities on the international stage, for instance treaty-making. A State is composed by governmental departments and representatives that testify their engagement through records, such as memories and opinions, publications and manuals. National legislation is also relevant to repress war crimes and grave breaches of humanitarian law, as well as for the practice of universal jurisdiction. Similarly, the Study determines that military manuals are a rich source that cover a wide range of premises, and which are part of the internal legal rules of armed forces. They enforce a particular behaviour in specific situations of armed conflict. General orders and instructions usually emanate from a commander-in-chief, or from the commander of a relevant section. They do not necessarily reflect what States have actually done, but rather what States intend to do. A military manual may represent numerous precedents and therefore a substantial practice, reflected in the cases of the United Kingdom, Germany and United States. The Study contains a representative list of 52 military manuals from all parts of the world. Most of them were published between 1990 and 1995 as a result of the joint campaign launched by the United Nations and the ICRC to promote national implementation of international humanitarian law. Promulgating a military manual means that a State makes a contribution to shape international customary law.
The Study affirms that decisions of international courts are subsidiary sources of international law. They do not constitute State practice, nevertheless it stresses that a finding by an international court that a rule of customary international law exists institutes persuasive evidence to that effect, and influences the subsequent practice of States and international organizations. The Study also makes extensive use of the jurisprudence of the International Criminal Tribunal for the former Yugoslavia (ICTY) and the International Criminal Court (ICC) Statutes. Throughout the travaux preparatoires, it is clear that the intention behind the drafting of the Statutes was to stay within the framework of customary law. For instance, the ICTY Trial Chamber in Furundzija declared that “in many areas the Statute may be regarded as indicative of the legal views, i.e., opinio juris of a great number of States”. Similarly, in Tadic the ‘grave breaches’ of the Geneva Conventions are also central, as is their application to non-international armed conflict. Consequently, in the drafting of the Rome Statute there was general agreement that the definitions of crimes in the jurisdiction of the ICC were to reflect existing customary international law.
The United Nations Secretary-General report on the International Criminal Tribunal for Rwanda gave an account of the appraisal of its customary status, with the drafting assistance of the United States and New Zealand. However, resolutions of the General Assembly, as in the present case, often entail disputes concerning their binding capacity, and a negative answer is regarded by some as synonym of irrelevance. In the General Assembly, despite its lack of legislative authority, the recommendations issued are often applied with significant relevance as exemplified in the Universal Declaration of Human Rights. This matter of capacity was also addressed by the ICJ in the Namibia case, and it was found that the General Assembly resolutions, while manifestly not binding, where “not without legal effect” given the existence of a right to terminate and monitor the mandate. The Court defined the recommendatory powers of the General Assembly as determinations with an operative design, in interpretation of the Charter of the United Nations, and as applicable as to their function. The ICJ defined this repeated practice in interpreting the treaty as establishing practice, that if the treaty concerns matters of international law, it can ultimately “harden into custom”. Nonetheless, it is also recognized that General Assembly resolutions cannot be a ‘substitute’ for ascertaining custom. A source of definition before such conflicts can be the analysis of the subject-matter of the resolution in question, their binding or recommendatory nature, the majorities supporting the adoption, and the repeated practice in relation to them as evidence of opinio juris. For this purpose, a list containing the voting records of all cited General Assembly resolutions was included in the Study.
ICRC statements are enclosed to the Study because of the international legal personality that the Committee enjoys. As seen in the 1965 Vienna 20th International Conference, with the adoption of Resolution XXVIII, which declared numerous common provisions as to those of the Study, it was soon reaffirmed by the General Assembly Resolution 2444. These principles have since been recognised as belonging to customary law. Nevertheless, these statements of the ICRC in the Study are never primary sources of evidence supporting customary law. NGOs statements are included in the second volume under ‘other practice’, and as a residual category without any influence in the determinations of custom. Thus, the relevant practice is the one cited in each rule.
Concerning the United States of America, reports and statements are analysed with respect to targeting decisions in the Korean, Vietnam and the Gulf War. Operational practice is also connected to military operations. Concerning the Protocols, the US is party to the second although not the first, and Amended Protocol II to the Convention on Certain Conventional Weapons, which contains a number of rules identical to the first non-ratified Protocol, and thus the US has supported the principle of distinction and proportionality that applies to international and non-international armed conflicts by signing this treaty and through its support to the work of the ad hoc international criminal tribunals.
Since the Geneva Conventions and Protocols, the ICRC Study represents the most notable achievement in humanitarian law. The United States reticence on the legal effects of the Study is blueprinted by their practise and policies, which are a result of their current preoccupations. The wars that are analysed in the ICRC Study that define the opinio juris and state practise of the United States of America are evidence of an extremely different period and geo-interests. In Korea or Vietnam there were no asymmetric challenges that would press the ‘drone’ priorities. The Cold War was based on a deterrence that is contrary to the current need for justifying ‘surgical’ operations in failed or rogue states. The difference of the contexts is specially manifested considering the Advisory Opinion on the Legality of the Threat of Nuclear Weapons, which is the one and only application possible to the role of the persistent objector, contrary to what the United States of America claim. The framework imposed by international law is based on a matter of ‘intentionality’ and ‘crystallisation’ on behalf of the ‘virtual’ majority of states that defines the binding capacity of the unwritten rules of customary law. In this respect if the rules are evident enough, there should be not a need for their compilation. On the other hand, perhaps for a compilation of customary law in the next century the US opinion can be compiled as evidence, since custom, by definition, is the law ‘as it’s been’, and not ‘the law that is to be’.
 Herein after: ‘Study’.
 J. Bellinger & W. Haynes, A US government response to the International Committee of the Red Cross study Customary International Humanitarian Law, 866 Reports and Documents of the International Review of the Red Cross, Vol. 89 (2007) 443 et seq.
 Statute of the International Court of Justice; for instance at: Statute of the International Court of Justice, at M. Evans, International Law Documents, Oxford University Press 8ed. (2007) 30 et seq; H. Thirlway, The Sources of International Law, in M. Evans (ed.), International Law, 2nd ed., Oxford (2006) 121 et seq.
 North Sea Continental Shelf Case (Denmark/The Netherlands v. Federal Republic of Germany), Judgement of 20 February 1969, 1960 ICJ Rep. at 3.
 Case Concerning Military and Paramilitary Activities in and against Nicaragua (Nicaragua v. United States of America), Merits, Judgment of 27 June 1986, 1986 ICJ Rep, at 14.
 North Sea Continental Shelf Cases (Denmark/The Netherlands v. Federal Republic of Germany), Judgement of 20 February 1969, 1960 ICJ Rep. at 3.
 Case Concerning Right of Passage Over Indian Territory (Portugal v. India), Merits, Judgment of 12 April 1960, 1960 ICJ Rep. at 6.
 Asylum Case (Colombia v. Peru), Judgment of the 20 November 1950, 1950 ICJ Rep. at 266.
 Fisheries Case (United Kingdom v. Norway) Judgment of 18 December 1951, 1951 ICJ Rep. at 116.
 J. Henckaerts & L. Doswald-Beck, Customary International Humanitarian Law, ICRC Cambridge University Press (2005); See also: C. Greenwood, The Law of War (International Humanitarian Law) in: M. Evans, (ed.), International Law, 2nd ed., Oxford (2006) 789 et seq and the Geneva Conventions of 1949, with Additional Protocol I and Additional Protocol II.
 J. Henckaerts & L. Doswald-Beck, Customary International Humanitarian Law, ICRC Cambridge University Press (2005) at 28.
 Furundzija Case: Judgment of the Trial Chamber, JL/PIU/372-E, 10 December 1998.
 Tadic Case: Judgment of the Appeals Chamber, H/ P.I.S./ 419-e, 15 July 1999.
 Statute of the International Tribunal for the Prosecution of Persons Responsible for Serious Violations of International Humanitarian Law Committed in the Territory of the Former Yugoslavia since 1991 (1993) UNSC Res.827 at M. Evans, International Law Documents, Oxford University Press 8ed. (2007) 352 et seq; Rome Statute of the International Criminal Court, at M. Evans, International Law Documents, Oxford University Press 8ed. (2007) 30 et seq.
 South West Africa Cases (Ethiopia/Liberia v. South Africa) Advisory Opinion, Judgment of 21 December 1962, 1962 ICJ Rep. at 319.
 J. Henckaerts & L. Doswald-Beck, Customary International Humanitarian Law, ICRC Cambridge University Press (2005).
 J. Henckaerts & L. Doswald-Beck, Customary International Humanitarian Law, ICRC Cambridge University Press (2005).
 Further relevant scholarly debate can be found, for instance, in: D. Turns, Weapons in the ICRC Study on Customary International Humanitarian Law, 2 Journal of Conflict & Security Law, Vol. 11 (2006) 201 et seq; F. Kalshoven & L. Zegveld, Constraints on the Waging of War. Geneva; International Committee of the Red Cross (2001); B. Jia, Customary International Humanitarian Law, 2 Chinese Journal of International Law, Vol. 4 (2005) 739 et seq; M. Bothe, Customary International Humanitarian Law, 8 Yearbook of International Humanitarian Law 143 et. seq. (2005); R, Cryer, Of Custom, Treaties, Scholars and the Gavel: The Influence of the International Criminal Tribunals on the ICRC Customary Law Study, 2 Journal of Conflict & Security Law, Vol. 11 (2006) 239 et seq; A. Cassese, The Geneva Protocols of 1977 on the Humanitarian Law of Armed Conflict and Customary International Law, UCLA Pacific Basin Law Journal (1984) 57 et seq; Y. Dinstein, The ICRC Customary International Humanitarian Law Study, 82 Int’l L. Stud. Ser. US Naval War Col. 99 (2006) 99 et seq; Y. Dinstein, The Interaction Between Customary International Law and Treaties, 322 Recueil des Cours 243 (2006) 383 et seq; K. Dormann & L. Maresca, Louis, The International Committee of the Red Cross and Its Contribution to the Development of International Humanitarian Law in Specialized Instruments, 5 Chicago Journal of International Law (2005) 217 et seq; D. Fleck, The Impact of the ICRC Study, 2 Journal of Conflict & Security Law Vol. 11 (2006) 179 et seq; J. Henckaerts, Customary International Humanitarian Law: a response to US comments, 866 Reports and Documents of the International Review of the Red Cross, Vol. 89 (2007) 473 et seq; L. Hogue, Identifying Customary International Law of War in Protocol I: A Proposed Restatement, Loyola of Los Angeles International & Comparative Law Review, Vol.13 (1991) 279 et seq; T. Meron, The Geneva Conventions as Customary Law, 81 American Journal of International Law (1987) 348 et seq; W. Parks, The ICRC Customary Law Study: A Preliminary Assessment, 99 American Society of International Law (2005) 208 et seq; J. Paust, The Importance of Customary International Law During Armed Conflict, 12 ILSA Journal of International & Comparative Law (2006) 601 et seq; P. Rowe, The Effect on National Law of the Customary International Humanitarian Law Study, 2 Journal of Conflict & Security Law Vol. 11 (2006) 165 et seq.