The Allied powers publicly announced that those responsible for atrocities would be punished after the war. The Moscow Declaration set an early distinction between lower-level perpetrators, to be tried where crimes occurred, and “major criminals,” whose crimes had no single location. This framing later supported a new legal approach to leadership responsibility for aggressive war and related atrocities.
The United States, United Kingdom, France, and USSR signed the London Agreement establishing the International Military Tribunal (IMT). Its attached Charter defined “crimes against peace,” including planning, preparing, initiating, or waging a war of aggression, and made individuals—especially leaders and organizers—criminally responsible. This was a major step in turning just war ideas about unlawful war into enforceable criminal law.
The IMT indictment was filed in Berlin against 24 major Nazi leaders and named several organizations as criminal. It charged conspiracy/common plan and “crimes against peace,” alongside war crimes and crimes against humanity. By putting aggressive war at the center, the indictment set up the courtroom debate over whether starting an illegal war could be punished as an international crime.
The IMT opened at the Palace of Justice in Nuremberg, with defendants entering pleas (generally “not guilty”). The court’s multinational structure and simultaneous translation aimed to give the proceedings legitimacy and fairness. This opening marked the start of sustained legal argument about individual responsibility for aggressive war, not just battlefield conduct.
U.S. chief prosecutor Robert H. Jackson argued that the case focused on “crimes against the peace,” stressing that the war was planned and prepared rather than accidental. He connected aggressive war to the other crimes by presenting it as the enabling act that made widespread atrocities possible. This helped shape the just-war-informed narrative that unlawful war is a root wrong with cascading harms.
The Allied Control Council issued Law No. 10 to create a uniform legal basis in occupied Germany for trying additional suspects beyond the IMT. It recognized “crimes against peace,” including planning and initiating wars of aggression, and provided a framework for later trials in different occupation zones. This institutional step broadened the reach of the aggressive-war concept beyond the headline Nuremberg case.
In its judgment on crimes against peace, the IMT stated that war is “essentially an evil thing” and concluded that initiating a war of aggression is “the supreme international crime” because it contains the accumulated evil of the whole. This language became a foundational reference point for later legal debates about aggression and leadership culpability. It also tied just war reasoning to a clear legal condemnation of unlawful resort to war.
The IMT delivered verdicts against the major defendants, convicting most and acquitting a small number. The tribunal imposed death sentences and long prison terms, and it also ruled that certain Nazi organizations were criminal. The outcome reinforced the claim that leaders can be held personally responsible for aggressive war as well as other international crimes.
After the IMT’s sentences, ten condemned defendants were executed by hanging at Nuremberg; Hermann Göring avoided execution by suicide shortly before it was carried out. These events closed the first IMT case in practical terms and underscored that the tribunal’s judgment had real punitive consequences. The enforcement of sentences also shaped later arguments about deterrence and legitimacy in international criminal justice.
U.S. authorities began a series of follow-on trials in Nuremberg (the Nuremberg Military Tribunals) using Control Council Law No. 10. These cases tested how far “crimes against peace” liability could extend beyond top political leaders, including to military officers, judges, doctors, and industrialists. In practice, these trials contributed to a narrower focus on leadership-level responsibility for aggressive war.
The UN General Assembly unanimously affirmed the principles of international law recognized by the IMT Charter and the IMT judgment. This was an important institutional signal that the international community supported the legal framework used at Nuremberg, including the treatment of aggressive war as a punishable offense. The resolution helped move Nuremberg-style reasoning from a one-time tribunal toward broader international acceptance.
The UN General Assembly directed the newly created International Law Commission (ILC) to formulate the principles of international law recognized in the Nuremberg Charter and judgment. This shifted Nuremberg’s legal argumentation into a codification project: turning courtroom reasoning into clearer, portable statements of law. It also kept the aggressive-war concept on the international agenda even as Cold War politics complicated enforcement.
The last of the U.S.-run Subsequent Nuremberg Trials ended, completing twelve major cases under Law No. 10. These judgments often emphasized that “crimes against peace” convictions require meaningful policy-level participation—helping establish a “leadership” approach to aggressive-war liability. This conclusion marked the endpoint of the 1945–1949 Nuremberg courtroom era and left a legacy that later debates on the crime of aggression would revisit.
The Nuremberg Trials and legal argumentation about aggressive war (1945–1949)