1 Henckaerts, Jean-Marie and Doswald-Beck, Louise (eds), Customary International Humanitarian Law, Vol. 1: Rules, Cambridge University Press, Cambridge, 2005CrossRefGoogle Scholar (ICRC Customary Law Study), available at: https://ihl-databases.icrc.org/customary-ihl/eng/docs/v1 (all internet references were accessed in May 2022).

2 Yahli Shereshevsky, “Back in the Game: International Humanitarian Lawmaking by States”, Berkeley Journal of International Law, Vol. 37, No. 1.

3 See, e.g., Boothby, William H., Conflict Law, Springer, New York, 2014, p. 72CrossRefGoogle Scholar; Bellinger, John B. III and Padmanabhan, Vijay M., “Detention Operations in Contemporary Conflicts: Four Challenges for the Geneva Conventions and Other Existing Law”, American Journal of International Law, Vol. 105, No. 2, 2011, p. 205CrossRefGoogle Scholar; Crawford, Emily, “From Inter-state and Symmetric to Intrastate and Asymmetric: Changing Methods of Warfare and the Law of Armed Conflict in the 100 Years Since World War One”, Yearbook of International Humanitarian Law, Vol. 17, 2014, p. 112Google Scholar.

4 Rome Statute of the ICC, UN Doc. A/CONF.183/9, 17 July 1998 (entered into force 1 July 2002).

5 (“Staat heisst das kälteste aller kalten Ungeheuer”): Nietzsche, Friedrich, Also sprach Zarathustra, Ein Buch für Alle und Keinen, Naumann, Leipzig, 1903, p. 64Google Scholar.

6 Political Report of the Central Committee of the Russian Communist Party for the 11th Party Congress, presented by Vladimir I. Lenin, 27 March 1922.

7 See the very accurate description of Swiss and ICRC efforts to get a new compliance mechanism for IHL: Emmanuela-Chiara Gillard, “Promoting Compliance with International Humanitarian Law”, Chatham House Briefing, October 2016, pp. 3 and 5, with references. Legally, the consensus ideal is only foreseen for the International Conference of the Red Cross and the Red Crescent in Article 11(7) of the Statutes of the International Red Cross and Red Crescent Movement, 1986, as amended in 2016, and in Rule 19 of the Rules of Procedure of the International Red Cross and Red Crescent Movement, 1986, as amended in 1995; the consensus requirement also exists in disarmament fora.

8 ICRC, “No Agreement by States on Mechanism to Strengthen Compliance with Rules of War”, 10 December 2015, available at: https://www.icrc.org/en/document/no-agreement-states-mechanism-strengthen-compliance-rules-war; Helen Durham, “Strengthening Compliance with IHL: Disappointment and Hope”, Humanitarian Law & Policy Blog, 14 December 2018, available at: https://blogs.icrc.org/law-and-policy/2018/12/14/strengthening-compliance-with-ihl-disappointment-and-hope/; and ICRC, Strengthening Compliance with International Humanitarian Law: Concluding Report, 32IC/15/19.2, Geneva, October 2015, available at: https://rcrcconference.org/app//uploads/2015/04/32IC-Concluding-report-on-Strengthening-Compliance-with-IHL_EN.pdf.

9 See Protocol Additional (II) to the Geneva Conventions of 12 August 1949, and relating to the Protection of Victims of Non-International Armed Conflicts, 1125 UNTS 609, 8 June 1977 (entered into force 7 December 1978), Art. 1(1).

10 Sandoz, Yves, “Le demi-siècle des Conventions de Genève”, Revue internationale de la Croix-Rouge, Vol. 81, No. 834, 1999, p. 241Google Scholar (my translation).

11 See Convention on the Prohibition of the Use, Stockpiling, Production and Transfer of Anti-Personnel Mines and on Their Destruction, 2056 UNTS 211, 18 September 1997 (entered into force 1 March 1998) (the “Ottawa Convention”). On the “Ottawa Process”, see, generally, Stuart Maslen and Peter Herby, “An International Ban on Anti-Personnel Mines: History and Negotiation of the ‘Ottawa Treaty’”, International Review of the Red Cross, Vol. 38, No. 325, 1998, pp. 693–8.

12 See Convention on Cluster Munitions, 2688 UNTS 39, 30 May 2008 (entered into force 1 August 2010).

13 See, generally, for a critical but detailed assessment of expert processes, Petrov, Anton Orlinov, Expert Laws of War: Restating and Making Law in Expert Processes, Elgar, Cheltenham, 2020CrossRefGoogle Scholar.

14 Melzer, Nils, Interpretive Guidance on the Notion of Direct Participation in Hostilities under International Humanitarian Law, ICRC, Geneva, 2009, p. 9Google Scholar.

15 ICRC, The Montreux Document on Pertinent International Legal Obligations and Good Practices for States Related to Operations of Private Military and Security Companies During Armed Conflict, Montreux, 17 September 2008 (Montreux Document), p. 9, available at: https://shop.icrc.org/the-montreux-document-on-private-military-and-security-companies-pdf-en.html. See also International Institute of Humanitarian Law, The Copenhagen Process on the Handling of Detainees in International Military Operations. The Copenhagen Process: Principles and Guidelines, 2012, p. 1, para. II, available at: https://iihl.org/wp-content/uploads/2018/04/Copenhagen-Process-Principles-and-Guidelines.pdf.

16 Guidelines for Protecting Schools and Universities from Military Use During Armed Conflict, Global Coalition to Protect Education from Attack, 2014, available at: https://protectingeducation.org/wp-content/uploads/documents/documents_guidelines_en.pdf.

17 Zwanenburg, Marten, “Keeping Camouflage Out of the Classroom: The Safe Schools Declaration and the Guidelines for Protecting Schools and Universities from Military Use During Armed Conflict”, Journal of Conflict & Security Law, Vol. 26, No. 2, pp. 257 and 282–3Google Scholar.

18 See, e.g., ICRC, International Humanitarian Law and Challenges of Contemporary Armed Conflicts, Geneva, October 2011, pp. 21–2 and 48–53, available at: https://www.icrc.org/en/doc/resources/documents/report/31-international-conference-ihl-challenges-report-2011-10-31.htm. See, also, “Procedural Principles and Safeguards for Internment/Administrative Detention in Armed Conflict and Other Situations of Violence”, as Annex 1 to ICRC, International Humanitarian Law and the Challenges of Contemporary Armed Conflicts, Document No. 30IC/07/8.4, Geneva, October 2007, published in International Review of the Red Cross, Vol. 87, No. 858, 2005.

19 ICRC, “Explosive Weapons: Civilians in Populated Areas Must be Protected”, 26 January 2022, available at: https://www.icrc.org/en/document/civilians-protected-against-explosive-weapons.

20 Sean Watts, “Interpretation in the Updated GCIII Commentary”, Articles of War, 15 December 2020, available at: https://lieber.westpoint.edu/interpretation-updated-gciii-commentary/; Michael W. Meier, “The Updated GCIII Commentary: A Flawed Methodology”, Articles of War, 3 February 2021, available at: https://lieber.westpoint.edu/updated-gciii-commentary-flawed-methodology/; Ronald Alcala, “Opinio Juris and the Essential Role of States”, Articles of War, 11 February 2021, available at: https://lieber.westpoint.edu/opinio-juris-essential-role-states/.

21 Schmitt, Michael N. and Watts, Sean, “State Opinio Juris and International Humanitarian Law Pluralism”, International Law Studies, Vol. 91, No. 1, 2015, p. 171Google Scholar.

22 Sassòli, Marco, International Humanitarian Law: Rules, Controversies, and Solutions to Problems Arising in Warfare, Edward Elgar, Cheltenham, 2019, p. 45CrossRefGoogle Scholar. See also Michael Bothe, Karl Joseph Partsch and Waldemar A. Solf, New Rules for Victims of Armed Conflicts: Commentary on the Two 1977 Protocols Additional to the Geneva Conventions of 1949, 2nd ed., Martinus Nijhoff, Leiden, 2013, pp. xxii and 7; Nicolas Michel, “Propos introductif. Le droit international humanitaire, entre frustrations, réussites et interrogations”, in Jean-François Flauss (ed.), Les nouvelles frontières du droit international humanitaire, Bruylant, Brussels, 2003, p. 13.

23 ICRC, Strengthening International Humanitarian Law Protecting Persons Deprived of Their Liberty: Concluding Report, Document No. 32IC/15/19.1, Geneva, October 2015, available at: https://rcrcconference.org/app/uploads/2015/04/32IC-Concluding-report-on-persons-deprived-of-their-liberty_EN.pdf.

24 UNGA Resolution 70/291, 15 June 2017; UNSC Resolution 2469, 28 March 2019, para. 24.

25 International Convention for the Protection of All Persons from Enforced Disappearance, 2716 UNTS 3, 20 December 2006 (entered into force 23 December 2010).

26 Convention on the Rights of Persons with Disabilities, 2515 UNTS 3, 13 December 2006 (entered into force 3 May 2008).

27 Optional Protocol to the Convention Against Torture and Other Cruel, Inhuman or Degrading Treatment or Punishment, 2375 UNTS 237, 18 December 2002 (entered into force 22 June 2006).

28 Forsythe, David P., The Humanitarians: The International Committee of the Red Cross, Cambridge University Press, Cambridge, 2005, pp. 251–2CrossRefGoogle Scholar.

29 In 1949, the International Law Commission refused to codify IHL because “public opinion might interpret its action as showing lack of confidence in the efficiency of the means at the disposal of the United Nations for maintaining peace”. See International Law Commission, Yearbook of the International Law Commission, 1949, p. 281.

30 See International Convention for the Protection of All Persons from Enforced Disappearance, above note 25; Convention on the Rights of Persons with Disabilities, above note 26; Optional Protocol to the Convention Against Torture and Other Cruel, Inhuman or Degrading Treatment or Punishment, above note 27.

31 Convention on Prohibitions or Restrictions on the Use of Certain Conventional Weapons Which May be Deemed to be Excessively Injurious or to Have Indiscriminate Effects (and Protocols), 1342 UNTS 137, 10 October 1980 (entered into force 2 December 1983); Protocol on Explosive Remnants of War to the Convention on Prohibitions or Restrictions on the Use of Certain Conventional Weapons Which May be Deemed to be Excessively Injurious or to Have Indiscriminate Effects (Protocol V), 2399 UNTS 100, 28 November 2003 (entered into force 12 November 2006).

32 Optional Protocol to the Convention on the Rights of the Child on the Involvement of Children in Armed Conflict, 2173 UNTS 222, 25 May 2000 (entered into force 12 February 2002).

33 Protocol Additional to the Geneva Conventions of 12 August 1949, and Relating to the Adoption of an Additional Distinctive Emblem (Protocol III), 2404 UNTS 261, 8 December 2005 (entered into force 14 January 2007).

34 See, generally, Ritu Mathur, Red Cross Interventions in Weapons Control, Lexington Books, New York, 2017.

35 ICRC, “Nuclear Weapons: Overdue Debate on Long-Term Impact Begins”, 13 February 2014, available at: https://www.icrc.org/en/doc/resources/documents/news-release/2014/02-11-mexico-nayarit-impact-nuclear-weapon-conference.htm; ICRC, “Why States Must Sign and Ratify the Treaty on the Prohibition of Nuclear Weapons: A Plea for Humanity”, Speech given by Mr. Peter Maurer, President of the ICRC, at the signing ceremony of the Treaty on the Prohibition of Nuclear Weapons, UN, New York, 26 September 2018, available at: https://www.icrc.org/en/document/icrc-president-why-states-must-sign-ratify-treaty-prohibition-nuclear-weapons-plea-humanity; ICRC, “Urgency to Rid the World of Most Destructive Weapon Ever Created”, 27 September 2018, available at: https://www.icrc.org/en/document/icrc-statement-high-level-plenary-meeting-commemorate-international-day-total-elimination; Robert Mardini, “Op Ed: Nuclear Weapons are Finally Outlawed; Next Step is Disarmament”, 22 January 2021, available at: https://www.icrc.org/en/document/nuclear-weapons-are-finally-outlawed-next-step-disarmament.

36 See ICRC, above note 23.

37 ICRC, “Strengthening IHL Protecting Persons Deprived of Their Liberty in Relation to Armed Conflict”, 1 April 2017, available at: https://www.icrc.org/en/document/detention-non-international-armed-conflict-icrcs-work-strengthening-legal-protection-0.

38 ICRC, “A Date to Remember: The Banning of Nuclear Weapons in 2021”, 21 January 2021, available at: https://www.icrc.org/en/document/date-remember-banning-nuclear-weapons-2021.

39 ICRC, “Autonomous Weapons: The ICRC Recommends Adopting New Rules”, 3 August 2021, available at: https://www.icrc.org/en/document/autonomous-weapons-icrc-recommends-new-rules.

40 See ICRC, “The ICRC in WWI: Efforts to Ban Chemical Warfare”, 11 January 2005, available at: https://www.icrc.org/en/document/icrc-wwi-efforts-ban-chemical-warfare.

41 See Herby, Peter, “1997: The Year of a Treaty Banning Anti-Personnel Mines?”, International Review of the Red Cross, Vol. 37, No. 317, 1997, pp. 193–5CrossRefGoogle Scholar.

42 See, generally, Hermida, Julian, “Convergence of Civil Law and Common Law Contracts in the Space Field”, Hong Kong Law Journal, Vol. 34, No. 2, 2004Google Scholar. See, also, Dainow, Joseph, The Civil Law and the Common Law: Some Points of Comparison, American Journal of Comparative Law, Vol. 15, No. 3, 1966–1967, pp. 424–6CrossRefGoogle Scholar.

43 I myself still wrote so in Marco Sassòli, “International Humanitarian Law and International Human Rights Law”, in Ben Saul and Dapo Akande (eds), The Oxford Guide to International Humanitarian Law, Oxford University Press, Oxford, 2020, p. 399.

44 See International Criminal Tribunal for the former Yugoslavia, The Prosecutor v. Tadić, Case No. IT-94-1-A, Decision on Jurisdiction (Appeals Chamber), 2 October 1995, paras 96–126 and 128–36, and Judgment (Appeals Chamber), 15 July 1999, paras 115–45 and 163–9, respectively.

45 For criticism of the Interpretive Guidance, see Watkin, Kenneth, “Opportunity Lost: Organized Armed Groups and the ICRC ‘Direct Participation in Hostilities’ Interpretive Guidance”, New York University Journal of International Law and Politics, Vol. 42, No. 3, 2010Google Scholar; Michael N. Schmitt, “The Interpretive Guidance on the Notion of Direct Participation in Hostilities: A Critical Analysis”, Harvard National Security Journal, Vol. 1, 2010; W. Hays Parks, “Part IX of the ICRC ‘Direct Participation in Hostilities’ Study: No Mandate, No Expertise, and Legally Incorrect”, New York University Journal of International Law and Politics, Vol. 42, 2010.

46 For a detailed criticism of the Tadic decisions, see Marco Sassòli, “La première décision de la Chambre d'appel du Tribunal pénal international pour l'ex-Yougoslavie: Tadic (compétence)”, Revue générale de droit international public, Vol. 100, 1996, pp. 101–34; and Sassòli, Marco and Olson, Laura M., “The Decision of the ICTY Appeals Chamber in the Tadic Case: New Horizons for International Humanitarian and Criminal Law?”, International Review of the Red Cross, Vol. 82, No. 839, 2000, pp. 733–69CrossRefGoogle Scholar.

47 See, e.g., Kretzmer, David and Ronen, Yaël, The Occupation of Justice: The Supreme Court of Israel and the Occupied Territories, 2nd ed., Oxford University Press, Oxford, 2021CrossRefGoogle Scholar.

48 See, e.g., United States Supreme Court, Salim Ahmed Hamdan v. Donald H. Rumsfeld et al., 548 U.S. 557 (2006), No. 05.184, 29 June 2006.

49 Weill, Sharon, The Role of National Courts in Applying International Humanitarian Law, Oxford University Press, Oxford, 2014, pp. 69–81CrossRefGoogle Scholar.

50 Ibid., pp. 13–67; D. Kretzmer and Y. Ronen, above note 47, p. 190.

51 S. Weill, above note 49, p. 67.

52 ICRC, Prevention Policy, Geneva, 2010, p. 7; ICRC, “Implementing International Humanitarian Law: From Law to Action”, Legal Factsheet, 2019.

53 ILO Declaration on Fundamental Principles and Rights at Work, 18 June 1998, para. 2.

54 Maupain, Francis, “Revitalization Not Retreat: The Real Potential of the 1998 ILO Declaration for the Universal Protection of Workers’ Rights”, European Journal of International Law, Vol. 16, No. 3, 2005, p. 451CrossRefGoogle Scholar.

55 Alston, Philip, “‘Core Labour Standards’ and the Transformation of the International Labour Rights Regime”, European Journal of International Law, Vol. 15, No. 3, 2004, p. 488CrossRefGoogle Scholar.

56 F. Maupain, above note 54, pp. 458–63.

57 Ibid.

58 Ibid., p. 460.

59 Ibid., p. 452, citing P. Alston, above note 55, pp. 518–20.

60 Ibid., pp. 453–4.

61 Ibid.

62 The text of the decision and the agreement as an annex may be found in UN, Adoption of the Paris Agreement, UN Doc. FCCC/CP/2015/L.9/Rev.1, 12 December 2015.

63 Laurence Poisson de Chazournes, “Regards sur l'Accord de Paris – un accord sur le futur”, in Marta Torre-Schaub (ed.), Bilan et perspectives de l'Accord de Paris (COP 21) – Regards croisés, Institut de la recherche juridique de la Sorbonne, Paris, 2017, p. 97.

64 Paris Agreement, 12 December 2015 (entered into force 4 November 2016), Art. 4.

65 See UN, Adoption of the Paris Agreement, above note 62, paras 134–7 of the Decision.

66 See, e.g., Ezgi Ediboğlu, “The Paris Agreement: Effectiveness Analysis of the New UN Climate Change Regime”, University College Dublin Law Review, Vol. 17, 2017.

67 E.g., Article 48 of Protocol I, reading, “In order to ensure respect for and protection of the civilian population and civilian objects, the Parties to the conflict shall at all times distinguish between the civilian population and combatants and between civilian objects and military objectives and accordingly shall direct their operations only against military objectives”, which should be acceptable also for States not parties to Protocol I, or Article 27 of Convention IV, where the technical term “protected persons” could be replaced either by civilians or by all persons who are in the power of a party.

68 ICJ, Pulp Mills on the River Uruguay (Argentina v. Uruguay), Judgment, ICJ Reports 2010, 20 April 2010, p. 14, para. 205.

69 The Optional Protocol to the Convention Against Torture and Other Cruel, Inhuman or Degrading Treatment or Punishment, above note 27, foresees a similar obligation to create a national mechanism, mainly for the purpose of monitoring the treatment of persons deprived of their liberty (Art. 17), but also to “to submit proposals and observations concerning existing or draft legislation” (Art. 19(c)).

70 See Blum, Gabriella, “On a Differential Law of War”, Harvard International Law Journal, Vol. 52, No. 1, 2011Google Scholar; and Heller, Kevin Jon, “On a Differential Law of War: A Response”, Harvard International Law Journal Online, Vol. 52, 2011Google Scholar.

71 See Sassòli, Marco, “Introducing a Sliding-Scale of Obligations to Address the Fundamental Inequality Between Armed Groups and States?”, International Review of the Red Cross, Vol. 93, No. 882, 2011Google Scholar.

72 See, for the monitoring and “reporting” mechanism to combat six grave violations committed against children in armed conflict established by the UNSC, the website of the Office of the Special Representative of the Secretary-General for Children and Armed Conflict, “Monitoring and Reporting on Grave Violations”, available at: https://childrenandarmedconflict.un.org/our-work/monitoring-and-reporting.

73 See, e.g., the UK initiative and the follow-up debate, “Preventing Sexual Violence in Conflict Initiative”, Hansard, Vol. 697, debated on 17 June 2021, available at: https://hansard.parliament.uk/commons/2021-06-17/debates/55A96907-C7BC-4865-8E74-978F14A461F8/PreventingSexualViolenceInConflictInitiative. See also, European Commission, Call to Action on Protection from Gender-Based Violence in Emergencies, Brussels, 2019, available at: https://ec.europa.eu/echo/system/files/2019-05/booklet_eu_leadership_c2a.pdf.

74 UNSC Resolution 2286, 3 May 2016.

75 Rondeau, Sophie, “Participation of Armed Groups in the Development of the Law Applicable to Armed Conflicts”, International Review of the Red Cross, Vol. 93, No. 883, 2011CrossRefGoogle Scholar.

76 ICRC, Annual Report 2020, Vol. I, p. 69, available at: https://library.icrc.org/library/docs/DOC/icrc-annual-report-2020-1.pdf.

77 Herbet, Irénée and Drevon, Jérôme, “Engaging Armed Groups at the International Committee of the Red Cross: Challenges, Opportunities and COVID-19”, International Review of the Red Cross, Vol. 915, No. 102, 2022Google Scholar.

78 See Geneva Call's website, available at: http://www.genevacall.org.

79 See Marco Sassòli, “The Convergence of the International Humanitarian Law of Non-International and of International Armed Conflicts: Dark Side of a Good Idea”, in Giovanni Biaggini, Oliver Diggelmann and Christine Kaufmann (eds), Polis und Kosmopolis, Festschrift für Daniel Thürer, Dike/Nomos, Zürich/Baden-Baden, 2015, pp. 683–4.

80 See M. Sassòli, above note 22, p. 285.

81 See ibid., p. 294.

82 The counterexample often mentioned, the admission of national liberation movements to the diplomatic conference which elaborated between 1974 and 1977 the Additional Protocols, has been very controversial and can only be explained by the particular historical situation: see M. Bothe, K.-J. Partsch and W. Solf, above note 22, p. 8.

83 See, e.g., ICRC, Safeguarding the Provision of Health Care: Operational Practices and Relevant International Humanitarian Law Concerning Armed Groups, Geneva, 2015; Geneva Call, In Their Words: Armed Non-State Actors Share Their Policies and Practice with Regards to Education in Armed Conflict, Geneva, 2017.

84 Thus, categorically, the International Law Commission, Draft Conclusions on Identification of Customary International Law, see International Law Commission, Report of the International Law Commission on the Work of its 68th Session, UN Doc. A/71/10, 2006, pp. 87–9, Conclusion 4(3) and para. 9 commentary to Conclusion 4. However, the ILC admits that it may provoke State practice, which is obviously a different issue.

85 J.-M. Henckaerts and L. Doswald-Beck, above note 1, p. xxxvi.

86 For further details, see Marco Sassòli, Bedeutung einer Kodifikation für das allgemeine Völkerrecht, Helbing & Lichtenhahn, Basel, 1990, pp. 32–48.

87 For this purpose, the Geneva Academy of International Humanitarian Law and Human Rights and Geneva Call have undertaken since 2017 a research project “From Words to Deeds: A Study of Armed Non-State Actors’ Practice and Interpretation of International Humanitarian and Human Rights Norms”. See research outcomes until now: Geneva Academy of International Humanitarian Law and Human Rights, “From Words to Deeds: A Study of Armed Non-State Actors’ Practice And Interpretation of International Humanitarian and Human Rights Norms”, available at: https://www.geneva-academy.ch/research/our-clusters/non-state-actors/detail/55-from-words-to-deeds-a-study-of-armed-non-state-actors-practice-and-interpretation-of-international-humanitarian-and-human-rights-norms.

88 See Lizaveta Tarasevich, “Participation of Non-State Armed Groups in the Formation of Customary International Humanitarian Law: Arising Challenges and Possible Solutions”, Humanitäres Völkerrecht, Journal of International Law of Peace and Armed Conflict, Vol. 3, No. 1–2, 2020.

89 Daboné, Zakaria, Le droit international public relatif aux groupes armés non étatiques, Schulthess, Geneva, 2012, pp. 87–8Google Scholar.

90 Roberts, Anthea and Sivakumaran, Sandesh, “Lawmaking by Nonstate Actors: Engaging Armed Groups in the Creation of International Humanitarian Law”, Yale Journal of International Law, Vol. 37, No. 1, 2011, pp. 141–52Google Scholar.

91 See Geneva Academy of International Humanitarian Law and Human Rights above note 87.

92 See, however, the forthcoming PhD of Ms Lizaveta Tarasevich at the University of Geneva on non-State armed groups and the formation of customary international law and her preliminary thoughts, above note 88.