War crimes

Definition published in the category International Crimes and Human Rights Violations

Last updated on 19 June 2026

War crimes are serious violations of international humanitarian law – whether treaty-based or customary – committed in both international and non-international armed conflict [1]. They cover a broad range of acts constituting violations of the laws of war as codified in the Lieber Code (1863) [2], the Hague Conventions of 1899 and 1907 [3], and the four Geneva Conventions adopted in 1949 [4], together with their Additional Protocols I and II [5].

The first known international war crimes trial was held by the Holy Roman Empire against the knight Peter von Hagenbach in the fifteenth century. It was followed in the twentieth century by the Leipzig War Crimes Trial for the crimes committed during the First World War and by the trials held by the Tokyo and Nuremberg Tribunals after the Second World War [6].

War crimes can be prosecuted before the International Criminal Court (ICC) [7]. The Rome Statute recognises the jurisdiction of the Court over crimes described as "grave breaches of the Geneva Conventions of 12 August 1949", "other serious violations of the laws and customs applicable in international armed conflict, within the established framework of international law" and "in the case of an armed conflict not of an international character, serious violations of article 3 common to the four Geneva Conventions of 12 August 1949" [8].

The Rome Statute – one of the most recent key references on war crimes – sets out a list of acts that can amount to war crimes, including several forms of sexual violence (rape, sexual slavery, enforced prostitution, forced pregnancy, enforced sterilisation or any other forms of sexual violence violating the laws of war either of international or non-international character) [9].

For conduct to qualify as a war crime, it must be committed in the context of and associated with an armed conflict (either international or non-international) [10]. The perpetrator must be aware of the existence of an armed conflict [11]. This means that incidental acts committed during a conflict cannot be prosecuted as war crimes.

This requirement has been a key issue in cases of sexual and gender-based violence (SGBV). Prior to the work of the International Criminal Tribunals for the former Yugoslavia (ICTY) and Rwanda (ICTR), acts of sexual violence were considered as incidental to conflicts and not as a strategic tool used by the parties to the conflict [12]. They were therefore not prosecuted as war crimes on the basis of a perceived lack of nexus to the conflict.

In several cases before the ad hoc tribunals and the ICC, judges have recognised the requisite nexus when acts of sexual violence were committed in parallel with military operations [13] and beyond. In the case of Dragoljub Kunarac, the ICTY judges held that "a violation of the laws or customs of war may [...] occur at a time when and in a place where no fighting is actually taking place" [14], and that "the armed conflict need not have been causal to the commission of the crime, but the existence of an armed conflict must, at a minimum, have played a substantial part in the perpetrator’s ability to commit it, his decision to commit it, the manner in which it was committed or the purpose for which it was committed" [15]. They found that rapes and other abuses were committed "as a direct result of the armed conflict and because the armed conflict apparently offered blanket impunity to the perpetrators" [16].

→ For an overview of forms of sexual and gender-based violence (SGBV) that may constitute war crimes, see the Policy on Gender-Based Crimes of the Office of the Prosecutor of the International Criminal Court (2023).

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Footnotes

[1] J-M. Henckaerts and L. Doswald-Beck, Customary International Humanitarian Law, Volume I: Rules, Cambridge: Cambridge University Press and International Committee of the Red Cross, 2005, Rule 156: Definition of War Crimes, pp. 568-604.

[2] Instructions for the Government of Armies of the United States in the Field (Lieber Code), 24 April 1863.

[3] Convention (II) with Respect to the Laws and Customs of War on Land and its annex: Regulations concerning the Laws and Customs of War on Land, The Hague, 29 July 1899; Convention (IV) respecting the Laws and Customs of War on Land and its annex: Regulations concerning the Laws and Customs of War on Land, The Hague, 18 October 1907.

[4] Convention (I) for the Amelioration of the Condition of the Wounded and Sick in Armed Forces in the Field ("Geneva Convention I"); Convention (II) for the Amelioration of the Condition of the Wounded, Sick and Shipwrecked Members of Armed Forces at Sea ("Geneva Convention II"); Convention (III) Relative to the Treatment of Prisoners of War ("Geneva Convention III"); Convention (IV) Relative to the Protection of Civilians in Time of War ("Geneva Convention IV"), Geneva, 12 August 1949 (collectively, the "Geneva Conventions").

[5] Protocol Additional (I) to the Geneva Conventions of 12 August 1949, and relating to the Protection of Victims of International Armed Conflicts ("Protocol I to the Geneva Conventions"), 8 June 1977; Protocol Additional (II) to the Geneva Conventions of 12 August 1949, and relating to the Protection of Victims of Non-International Armed Conflicts ("Protocol II to the Geneva Conventions"), 8 June 1977.

[6] International Crime Database, "War crimes", n.d.

[7] Rome Statute of the International Criminal Court ("Rome Statute"), A/CON.183/9, 17 July 1998, entered into force 1 July 2002, Articles 5 and 8.

[8] Ibid., Article 8.

[9] Idem.

[10] ICC, Elements of Crimes ("ICC Elements of Crimes"), 3-10 September 2002 (reviewed in 2010), Article 8.

[11] Idem.

[12] "Sexual violence in conflict needs to be treated as the war crime that it is; it can no longer be treated as an unfortunate collateral damage of war." Quote from former UN Special Representative on Sexual Violence in Conflict, Ms. Zainad Hawa Bangura, in United Nations, Sexual Violence: a Tool of War, Background note, 2014.

[13] For example, in the case of Brdanin, the appeals judges of the ICTY noted that rapes perpetrated during weapon searches were to be considered as committed in the context of the armed conflict. See ICTY, Prosecutor v. Radoslav Brdanin, Appeals Judgement, IT-99-36-A, 3 April 2007, para. 256: "Crimes committed by combatants and by members of forces accompanying them while searching for weapons during an armed conflict, and taking advantage of their position, clearly fall into the category of crimes committed ’in the context of the armed conflict’."

[14] ICTY, Prosecutor v. Dragoljub Kunarac, Radomir Kovac and Zoran Vukovic, Appeals Judgement, IT-96-23&IT-96-23/1-A, 12 June 2002, para. 57.

[15] Ibid., para. 58.

[16] ICTY, Prosecutor v. Kunarac, Kovac and Vukovic, Trial Judgment, IT-96-23-T, 22 February 2001, para. 568; For more examples on the nexus between acts of sexual violence, mainly rape, and armed conflict in determining whether or not a war crime has been committed, see M. Jarvis and S. Brammertz, Prosecuting conflict-related sexual violence at the ICTY, Oxford University Press, 2016, pp. 179-181.