By invading Ukraine in February, Russia committed a blatant war of aggression, evoking memories of the death and destruction of World War II. Not only was the very launching of the war illegal, but so, too, has been its prosecution. Over the last three months, Russian troops have killed thousands of civilians and laid waste to cities in Ukraine. As Ukrainian forces have begun retaking towns from Russian occupying forces, they have discovered mass graves and widespread evidence of other atrocities.

International institutions and an unprecedented coalition of states have taken early steps toward holding Russia accountable for these war crimes. The International Criminal Court (ICC) has launched an investigation, and it is already sending officials to Ukraine to gather evidence. But when it comes to prosecuting those most responsible for the most notorious crime—waging an aggressive war—there are no international venues for doing so.

That may seem surprising, given that this crime was the lead charge of the Nuremberg trials, in which Nazi officials were tried after World War II. Indeed, in its judgment, the International Military Tribunal at Nuremberg declared, “To initiate a war of aggression . . . is not only an international crime; it is the supreme international crime differing only from other war crimes in that it contains within itself the accumulated evil of the whole.”

Now, the world is once again witnessing “the supreme international crime.” To prosecute those responsible, it will be necessary to create an entirely new court. That should be done through an agreement between Ukraine and the UN, with the authorization of the General Assembly. Setting up such a court will not be easy, in no small part because it would require building a global consensus in a time of division. Yet doing so is essential to sustaining the postwar international legal order founded on the prohibition of war.


To understand the crime of aggression and its importance to the legal order, it is necessary to understand its history. World War II was a battle between states with diametrically opposed visions of the international legal order. In launching the war, Adolf Hitler pursued a policy of Lebensraum (literally, “living space”), contending that Germany needed more territory. The Allied countries took the opposite view: that wars of territorial conquest should not be tolerated. That policy had first been pronounced in the Kellogg-Briand Pact of 1928, also known as the Pact of Paris, in which the countries of the world agreed to renounce “war as an instrument of national policy.”

At the close of World War II, the victors debated how to establish criminal accountability for the war. Although some, including British Prime Minister Winston Churchill, advocated the summary execution of Germany’s leaders, the Allies decided to establish what would become known as the International Military Tribunal at Nuremberg. The indictment of 24 German political, military, and economic leaders marked the first time aggressive war was charged as a crime in an international court. The first count of the Nuremberg indictment charged the defendants with planning an aggressive war “in advance, in violation of the terms of the Kellogg-Briand Pact of 1928.” (Similar charges were made in the International Military Tribunal for the Far East in Tokyo, which tried Japanese leaders for starting and waging war.) This made the crime of aggression the foundational charge of the Nuremberg trial. Indeed, in the view of Robert Jackson, the chief U.S. prosecutor at Nuremberg and a U.S. Supreme Court justice, the Nazis could be prosecuted for crimes committed as part of the Holocaust only because it was part of an aggressive war waged in violation of the Kellogg-Briand Pact.

In the years since Nuremberg, it may seem puzzling that there have been no other international court cases charging the crime of aggression. There are two chief reasons for this, one hopeful and one less so. The hopeful reason is that the UN Charter was largely successful at significantly reducing, although not eliminating, aggressive war between sovereign states. The less hopeful reason is that after the Nuremberg and Tokyo tribunals were disbanded, no international court had jurisdiction over the crime. That was no coincidence. The most powerful countries, including the United States, had little interest in establishing a court that might subject their own military or civilian leaders to scrutiny.

The crime resurfaced five decades later, during negotiations over the Rome Statute, which would eventually give rise to the ICC in 2002. Many advocates of the court hoped to include the crime of aggression on the list of crimes that could be charged and prosecuted before it. But there was significant opposition. The crime was included in the founding treaty, but the details were left to be settled, and the crime could not be charged until they were.

The world is once again witnessing “the supreme international crime.”

In 2010, during a conference of the parties to the Rome Statute held in Kampala, Uganda, a definition was finally adopted. To reserve criminal liability for the most significant violations, the new definition provided that only “manifest” violations of the charter of the United Nations could be charged. Moreover, the crime was explicitly made a leadership crime—applicable only against a person engaged in “planning, preparation, initiation or execution” who was “in a position effectively to exercise control over or to direct the political or military action of a State.” Thus, the drafters attempted to avoid some of the controversy generated by the crime—and fears that it might be used against ordinary soldiers fighting in wars of debatable legality—by limiting it to those most responsible for unmistakably illegal wars.

The United States, participating as a nonparty in these negotiations, successfully advocated to further limit the circumstances under which these charges could be brought. Language was added so that the crime could not be applied against nationals of nonparties to the agreement, including the United States and Russia. In this respect, the crime of aggression differs from the other three crimes covered by the Rome Statute—war crimes, crimes against humanity, and genocide—all of which can be charged either against the nationals of a state that is a party to the ICC or if the crime is committed on the territory of a state that has agreed to the court’s jurisdiction.


Today, there is no doubt that Russia has waged an illegal war of aggression in Ukraine. Nor is there any doubt that those who have planned, prepared, initiated, and executed it are guilty of the crime of aggression. And yet the crime cannot be charged in the ICC. The reason, perhaps ironically, has to do with the concession made to the United States at Kampala: the crime cannot be applied against nationals of nonparties. With the ICC unable to charge Russians for the crime of aggression and no other existing international court with jurisdiction over the crime, the question now is whether and how there might be accountability for one of the most flagrant and dangerous violations of the UN Charter in modern history.

One possibility would be to rely on domestic prosecutions in Ukraine’s own courts. Aggression is a domestic crime in Ukraine. Indeed, the government prosecuted and convicted former President Viktor Yanukovych for treason and the crime of aggression for asking Russian President Vladimir Putin to send Russian troops to invade Ukraine after Yanukovych fled the country in 2014 (he was sentenced in absentia to 13 years in prison). But there are two problems with this approach. First, international law establishes immunity for foreign heads of state and foreign officials, preventing them from being prosecuted in the domestic courts of foreign states. (This was not a barrier to prosecuting Yanukovych, because he is Ukrainian.) Therefore, the very people most responsible for the crime of aggression, namely Putin and other senior Russian leaders, could not be prosecuted in Ukrainian courts. Second, Ukraine allows trials in absentia, which are generally regarded as inconsistent with international human rights principles that require defendants to have an opportunity to present a defense. Such trials also allow persons found guilty to evade justice by remaining outside the country. Indeed, Yanukovych remains free in Russia.

A leading alternative is to have a group of states, including Ukraine, create an ad hoc international court. Advocates cite the Nuremberg tribunal as a precedent. But they fail to note that the only option for providing legal accountability after World War II was to create a court under the authority of an ad hoc collection of states. Today, however, the world has the UN. If a court were now created by a self-appointed group of states, it would likely be viewed as an act of selective justice with little legitimacy. The precedent such an ad hoc court would set, moreover, should worry the U.S. government. If a small group of states can create a court to try the government officials of another state, what is to stop Russia and the four states that joined it in voting against a UN resolution condemning Russia’s invasion (Belarus, Eritrea, North Korea, and Syria) from establishing their own international court to try U.S. government officials?

Russia has challenged the fundamental principles for which the Allies fought in World War II.

The best option would be to establish a court through the UN. Since Nuremberg, all the international courts that have been established, except those that are expressly regional in scope, have involved some UN role. The International Criminal Tribunals for the Former Yugoslavia and Rwanda, for example, were both established by the UN in the early 1990s under the auspices of the Security Council in the wake of atrocity crimes in those countries.

For the current conflict, establishing a court through the UN Security Council is not an option, because Russia, as one of its five permanent members, would surely veto any such effort. But that is not the only option. A court could be established instead through an agreement between Ukraine and the UN, authorized by the General Assembly. There is precedent—the Extraordinary Chambers in the Courts of Cambodia was formed in 2002 by an agreement between Cambodia and the UN, authorized by the General Assembly. The definition of the crime of aggression adopted in the Rome Statute can and should be used in this new court—that definition, after all, was agreed to by a consensus of states that participated in the negotiations over the definition, including Russia.

An alternative would be to establish a court through an agreement between Ukraine and another existing international organization. Two that have recently been discussed are the EU and the Organization for Security and Cooperation in Europe. While better than a court formed by an ad hoc group of states, a court created by these European organizations would not have the moral or legal force of a court established by the UN and its global membership. Relying on these European international institutions makes it too easy for Russia to portray the conflict as simply one between Russia and the West rather than what it is—a conflict between Russia and all those who believe in a rules-based international order founded on the principle that states may not resort to the use of force against one another.


While the United States has had a turbulent relationship with the ICC, championing a new, narrowly focused court would allow the United States to reclaim the role it played at the close of World War II, when it emerged as a leading advocate of international justice. More, recently, Washington has supported a number of international courts—most notably the courts for the former Yugoslavia, Rwanda, Sierra Leone, and Cambodia—and it has even supported Security Council referrals of the situations in Libya and Syria to the ICC (although the latter was vetoed by Russia).

A court established through the UN with the authorization of the General Assembly and with the consent of Ukraine would require significant political consensus and would therefore be unlikely to create the worrisome precedent of an ad hoc or regional court. But this is also the hard part: getting buy-in from enough countries. Although 140 states voted in the UN to condemn Russia, far fewer voted to expel Russia from the Human Rights Council a month later. People across the globe have also noticed that Ukrainians are receiving an outpouring of support and assistance, even as those who have suffered from conflicts that have long raged elsewhere in the world are ignored. But that is precisely why working through the UN—and the General Assembly—is so crucial. A court that does not have support from states outside the “global North” would lack the very legitimacy essential for its success.

It is unlikely that Putin, who is clearly the man most responsible for the war, will ever be placed in the dock, even if such a court is established. But the creation of a court is not simply about holding one person—or a few—personally accountable. Russia has challenged the fundamental principles for which the Allies fought in World War II and the very core of the modern international legal order they established in its aftermath. If those principles are to survive Russia’s assault, the global community, working through the institution created after the war to keep the peace, must act—together with Ukraine—to reinforce and reaffirm those principles. If it does so, there is a chance that the international legal order will emerge from this crisis stronger than ever.

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