Creating an international criminal court had never been done before. The four powers had different legal traditions and different interests. In the summer of 1945, their lawyers had to agree on what crimes the court would judge, how it would work and where it would sit.

The negotiators

The American delegation was led by Robert H. Jackson, a justice of the US Supreme Court whom President Truman appointed as chief prosecutor. Jackson pushed hard for a trial that would define aggressive war itself as a crime. The negotiators had to bridge real differences. The British and Americans used common law, with adversarial trials in which prosecution and defense present cases to a neutral judge. The French and Soviets used civil law systems, in which judges play a more active role in investigating. The Soviets, moreover, were accustomed to trials whose outcomes were decided in advance.

The London Charter

On 8 August 1945, the four powers signed the London Charter, which established the International Military Tribunal. The charter set out three categories of crime.

• Crimes against peace: planning, preparing, starting or waging a war of aggression, or a war in violation of international treaties.
• War crimes: violations of the laws and customs of war, such as the murder or ill-treatment of prisoners of war or civilians in occupied territory, the killing of hostages and the wanton destruction of cities.
• Crimes against humanity: murder, extermination, enslavement, deportation and other inhumane acts against any civilian population, and persecution on political, racial or religious grounds.

The charter also made it a crime to take part in a common plan or conspiracy to commit these crimes, an idea drawn from American law that allowed the prosecution to tie together the actions of many leaders.

New ideas

Two of these categories broke new ground. War crimes had long been recognized in treaties such as the Hague Conventions of 1899 and 1907. But treating aggressive war as a crime for which individuals could be punished was new. So was “crimes against humanity,” which covered acts committed by a government against its own people, such as the persecution of German Jews before the war. Before Nuremberg, international law mostly dealt with how states treated each other; what a government did inside its own borders was largely its own affair. The charter asserted that some acts were crimes against all humanity, wherever and against whomever they were committed.

No hiding behind office or orders

Two articles of the charter shaped the trial profoundly. Article 7 declared that the official position of defendants, whether as heads of state or responsible officials, would not free them from responsibility or reduce their punishment. Article 8 declared that acting under orders from a superior would not free a defendant from responsibility, though it might be considered in reducing the punishment if justice required. Leaders could not say they were above the law, and subordinates could not say they were merely obeying.

Why Nuremberg?

The Soviets wanted the trial in Berlin, in their zone of occupation. The Americans favored Nuremberg, in their zone, for practical and symbolic reasons. Its Palace of Justice had survived the bombing largely intact and had a large prison attached. And Nuremberg was the city where the Nazi Party had held its huge annual rallies and where, in 1935, the regime had proclaimed the Nuremberg Laws, which stripped German Jews of citizenship and banned marriages between Jews and other Germans. Trying the Nazi leaders there carried a clear message. As a compromise, the tribunal held its first formal session in Berlin in October 1945, then moved to Nuremberg for the trial.

Worked example: is it fair to punish a new crime?

One of the oldest principles of justice holds that no one should be punished for an act that was not a crime when it was committed. The Latin phrase is nullum crimen sine lege, “no crime without law.” Apply it to the charge of crimes against peace.

• The objection. Before 1945, no treaty had stated that individual leaders could be punished for starting a war. Punishing them now seems to create a crime after the fact, which is exactly what fair legal systems forbid.
• The reply from treaties. In the Kellogg-Briand Pact of 1928, Germany and many other nations renounced war as an instrument of national policy. Aggressive war was therefore already illegal, even if punishment of individuals had not been spelled out.
• The reply from justice. The principle against retroactive law exists to protect people who could not have known their actions were wrong. Leaders who planned invasions of peaceful neighbors in violation of treaties could hardly claim that.
• The remaining doubt. Even if the defendants deserved punishment, critics argued that the court should not have stretched the law, because a precedent of stretching it could be abused later.

Both sides appealed to fairness. That is what makes the question hard. The tribunal sided with the replies, but the objection never disappeared, and it shaped later efforts to write international crimes into clear, agreed treaties before anyone was charged with them.