War Crimes: How International Law Defines and Prosecutes Atrocities

The Nuremberg Precedent Changed Everything

On October 1, 1946, the International Military Tribunal at Nuremberg sentenced twelve Nazi leaders to death and seven to prison terms, establishing for the first time that individuals — not only states — bear criminal responsibility under international law for acts committed during war. Before Nuremberg, international law was a system of rules between states; afterward, it became a system that could reach individual human beings regardless of their rank or nationality. That shift is the foundation of every war crimes prosecution that has followed.

The tribunal operated under the London Charter of August 1945, negotiated by the United States, United Kingdom, France, and the Soviet Union. It established three categories of international crime: crimes against peace, war crimes, and crimes against humanity. The Nuremberg principles were subsequently affirmed by the UN General Assembly in Resolution 95(I) of 1946 and codified, in revised form, in the Rome Statute of the International Criminal Court in 1998.

How War Crimes Differ from Genocide and Crimes Against Humanity

The three core categories of international crimes are related but legally distinct. Conflating them is the most common error in public discourse about atrocities.

A single act — killing one prisoner of war — can constitute a war crime without being either a crime against humanity or genocide. Conversely, genocide requires proof of specific intent (dolus specialis) that war crimes do not demand. The distinction matters for prosecution: proving genocide is significantly harder than proving war crimes because the mental element is more demanding.

Article 8 of the Rome Statute: The War Crimes List

The Rome Statute's Article 8 provides the most comprehensive codification of war crimes in international law. It is organized into four categories covering international and non-international armed conflicts. Key categories include:

• Grave breaches of the Geneva Conventions: willful killing, torture, inhumane treatment, unlawful deportation, taking hostages, extensive destruction of property unjustified by military necessity
• Other serious violations in international conflicts: attacking civilians or civilian objects, indiscriminate attacks, attacking humanitarian workers or UN peacekeepers, using prohibited weapons (poison, expanding bullets, chemical weapons), sexual violence including rape
• Serious violations in non-international conflicts: murder, mutilation, cruel treatment, collective punishments, attacking civilians, pillaging, rape and sexual violence
• Other serious violations in non-international conflicts: using children in hostilities, destroying civilian infrastructure, starvation as a method of warfare

The ICC has jurisdiction over Article 8 crimes only when they are "committed as part of a plan or policy or as part of a large-scale commission" — a threshold clause that narrows jurisdiction to systematic rather than isolated violations, though the Pre-Trial Chamber has interpreted this broadly.

Command Responsibility: When Generals Bear Criminal Liability

Individual criminal responsibility for war crimes extends beyond those who physically commit them. The doctrine of command responsibility — also called superior responsibility — holds that military commanders and civilian superiors can be convicted for crimes committed by subordinates under two conditions.

First, the commander must have known, or should have known, that subordinates were committing or about to commit crimes. Second, the commander must have failed to take all necessary and reasonable measures to prevent or punish those crimes. The doctrine does not require proof that the commander ordered the crimes — failure to act is sufficient.

The foundational case is In re Yamashita (1945), in which the US Supreme Court upheld the conviction and execution of Japanese General Tomoyuki Yamashita for atrocities committed by troops under his command in the Philippines, even though the prosecution did not prove he ordered the killings or had specific knowledge of them. The standard was controversial then and remains debated: it creates liability for negligence in supervision, which some argue is too expansive.

ICC Jurisdiction: Three Triggers

The International Criminal Court, established by the Rome Statute entering into force in 2002, does not have automatic universal jurisdiction. It can exercise jurisdiction over war crimes through three distinct mechanisms.

• State party referral: Any of the 124 state parties may refer a situation to the Prosecutor
• Prosecutor proprio motu: The Prosecutor may initiate investigations independently, subject to Pre-Trial Chamber authorization
• UN Security Council referral: The Security Council may refer situations involving any state, including non-parties, under Chapter VII of the UN Charter

The Security Council referral mechanism was used for Sudan (2005) and Libya (2011), enabling ICC jurisdiction over states that had not ratified the Rome Statute. However, permanent members — the United States, Russia, and China — are not ICC parties and have used or threatened vetoes to block referrals involving allied states.

The Pinochet Case and Universal Jurisdiction

In 1998, Chilean former dictator Augusto Pinochet was arrested in London on a Spanish extradition warrant for torture committed in Chile between 1973 and 1990. The UK House of Lords ruled in 1999 that Pinochet had no immunity for acts of torture because torture is an international crime for which no head-of-state immunity exists under customary international law. It was a landmark ruling. The principle that former heads of state enjoy no immunity from prosecution in foreign courts for international crimes was established — in theory.

Pinochet was ultimately returned to Chile on medical grounds without being extradited to Spain. But the legal principle survived the political outcome. The Pinochet litigation demonstrated that domestic courts could exercise universal jurisdiction — jurisdiction based solely on the gravity of the crime, regardless of where it was committed or the nationality of the perpetrator or victim.

The Erosion of Head-of-State Immunity

The Rome Statute explicitly rejects head-of-state immunity in Article 27, stating that official capacity "shall in no case exempt a person from criminal responsibility." The ICC issued arrest warrants for sitting heads of state: Omar al-Bashir of Sudan (2009), Muammar Gaddafi of Libya (2011), and Vladimir Putin of Russia (2023). None has been surrendered to the court.

The tension between legal principle and political reality defines contemporary international criminal law. The rules are clear and increasingly specific. Enforcement depends on state cooperation, political will, and the asymmetries of power that determine which actors are ever actually held accountable. The gap remains wide — but it is narrower than it was in 1945.