International criminal law

Lore & Background

International criminal law emerged after World War II when the Allied powers set up an international tribunal to try war crimes and crimes against humanity committed by Nazi Germany and Imperial Japan. The Nuremberg Tribunal held its first session in 1945 and pronounced judgments in 1946. A similar tribunal operated for Japanese war crimes from 1946 to 1948. After being dormant for decades, international criminal law was revived in the 1990s to address war crimes in the Yugoslav Wars and the Rwandan genocide, leading to the establishment of the International Criminal Court in 2002.

The sources of international criminal law are those of international law generally: treaties, customary international law,

Reader's Guide

International criminal law represents an attempt by the international community to address the most grievous atrocities, though it has not been an ideal instrument for making the fine distinctions typical of national law. Its core crimes—genocide, war crimes, crimes against humanity, and the crime of aggression—target large-scale conduct that 'shocks the conscience.' The prosecution of these crimes is considered necessary to enforce the law and deliver justice to victims, playing a role in transitional justice. However, impunity remains common: James Waller concludes that genocide is often worth it because chances of punishment are relatively inconsequential. For example, while several thousand SS soldiers were prosecuted after World War II, only 124 were convicted. The apprehension and conviction rates for international tribunals are equally disconcerting. The International Military Tribunal ruled in 1946 that aggression was 'the supreme international crime' because it contains within itself the accumulated evil of the whole.

Did You Know?

• The first attempt to establish an international criminal tribunal occurred as part of the Treaty of Versailles, targeting Wilhelm II, but was abandoned after he fled to the Netherlands.
• The International Criminal Court began operations after the Rome Statute entered into force in 2002, issuing its first arrest warrants in 2005.
• Genocide is defined by the 1948 Genocide Convention as five acts committed with intent to destroy a national, ethnical, racial, or religious group.
• Crimes against humanity do not have to take place within the context of wars and apply to widespread practices rather than individual acts.

From State Sovereignty to Individual Guilt

Before the mid-twentieth century, international law was essentially a framework governing how states interacted with one another—mapping out their rights, obligations, and diplomatic responsibilities. Individuals operated outside its reach. The Treaty of Versailles marked the first tentative step beyond that boundary, proposing that the deposed German emperor Wilhelm II face a panel of five allied judges. The scheme collapsed almost immediately: Wilhelm escaped to the Netherlands, a country that had not signed the treaty, and The Hague refused to hand him over. The true breakthrough came after World War II. The Charter of the International Military Tribunal and the subsequent Nuremberg proceedings shattered the old paradigm by holding the defeated leadership of Nazi Germany personally and criminally responsible for their actions. The tribunal convened its first session in 1945 and delivered its verdicts on September 30 and October 1, 1946. A parallel body, the International Military Tribunal for the Far East, operated from 1946 through 1948 to address atrocities committed by Imperial Japan. In doing so, these trials effectively invented a new legal discipline: international criminal law, in which the individual—not merely the state—could be brought to account for the gravest offenses.

The Four Pillars of Atrocity

International criminal law organizes its gravest offenses into four categories: genocide, war crimes, crimes against humanity, and the crime of aggression. War crimes stem from violations of the law of war treaties and attach individual criminal responsibility to conduct in armed conflict—deliberate killing, torture, rape, hostage-taking of protected persons, wanton destruction of civilian property, perfidy, and pillaging. Command-level actors face added liability for ordering mass killings or ethnic cleansing, refusing quarter to those who surrender, conscripting children, or disregarding proportionality and military necessity. Genocide, as defined by the 1948 United Nations Genocide Convention, requires intent to destroy a national, ethnic, racial, or religious group in whole or in part, expressed through killing, serious harm, destructive living conditions, prevention of births, or forced transfer of children. Crimes against humanity, by contrast, need not occur during wartime; they are widespread or systemic acts committed by or on behalf of a state or de facto authority that grossly violate human rights. The discipline deliberately forgoes the fine-grained distinctions of domestic criminal law, concentrating instead on large-scale atrocities that "shock the conscience." This focus produces notable analytical differences—especially around legal intent—between international and national legal systems.

The Long Road to a Permanent Court

For decades after the Nuremberg and Tokyo tribunals, international criminal law lay largely dormant. The field experienced a dramatic resurgence in the 1990s, driven by two catastrophic crises. When the war in Bosnia erupted, the United Nations Security Council established the International Criminal Tribunal for the Former Yugoslavia in 1993. The following year, in the wake of the Rwandan genocide, the International Criminal Tribunal for Rwanda was created. These ad hoc bodies demonstrated both the necessity and the limitations of temporary judicial mechanisms. Simultaneously, the International Law Commission began preparatory work in 1993 toward a standing, permanent court. That effort culminated in the Rome Statute, which entered into force in 2002, bringing the International Criminal Court into operational existence. The ICC issued its first arrest warrants in 2005, marking the beginning of a new era in which the international community could pursue atrocity crimes through a permanent institutional framework rather than assembling ad hoc tribunals for each crisis. The Special Court for Sierra Leone also illustrates the flexibility of the system, as it was empowered to apply national laws alongside international ones.

Sources, Legality, and the Justice-Principle Tension

As a subset of international law, international criminal law draws its authority from the same foundational sources enumerated in Article 38(1) of the 1946 Statute of the International Court of Justice: treaties, customary international law, general principles of law, and, as subsidiary measures, judicial decisions and the most highly qualified juristic writings. The Rome Statute governing the International Criminal Court contains an analogous but not identical set of sources the court may rely upon. In practice, the rules applied in any given case depend heavily on the presiding body. National courts may apply a different body of rules than an international tribunal, and specific tribunals may vary their approach depending on their own Statute. Yet a persistent tension runs through the field's history. The legal principle of nullum crimen sine lege—no crime without a prior law—has been flouted by numerous international criminal tribunals, which have convicted defendants of acts that were not criminal at the time they were committed. Critics argue this reflects a privileging of substantive justice over the principle of legality, raising enduring questions about the balance between punishing atrocity and respecting the rule of law.