A precedent for trying those accused of war crimes had been set at the end of World War I in the Leipzig War Crimes Trials held in May to July 1921 before the Reichsgericht (German Supreme Court) in Leipzig, although these had been on a very limited scale and largely regarded as ineffectual.
At the beginning of 1940, the Polish government-in-exile asked the British and French governments to condemn the German invasion of their country.
The British initially declined to do so; however, in April 1940, a joint declaration was issued by the British, French, and Polish.
Relatively bland because of Anglo-French reservations, it proclaimed the trio's "desire to make a formal and public protest to the conscience of the world against the action of the German government whom they must hold responsible for these crimes which cannot remain unpunished."

Three-and-a-half years later, the stated intention to punish the Germans was much more trenchant.
On 1 November 1943, the Soviet Union, the United Kingdom, and the United States published their "Declaration on German Atrocities in Occupied Europe", which gave a "full warning" that, when the Nazis were defeated, the Allies would "pursue them to the uttermost ends of the earth ... so that justice may be done.
 ... The above declaration is without prejudice to the case of the major war criminals whose offenses have no particular geographical location and who will be punished by a joint decision of the Government of the Allies."
This intention by the Allies to dispense justice was reiterated at the Yalta Conference and at Potsdam in 1945.

British War Cabinet documents, released on 2 January 2006, showed that as early as December 1944 the Cabinet had discussed their policy for the punishment of the leading Nazis if captured.
The British Prime Minister, Winston Churchill, had then advocated a policy of summary execution in some circumstances, with the use of an Act of Attainder to circumvent legal obstacles, being dissuaded from this only by talks with US and Soviet leaders later in the war.

In late 1943, during the Tripartite Dinner Meeting at the Tehran Conference, the Soviet leader, Joseph Stalin, proposed executing 50,000–100,000 German staff officers.
US President Franklin D. Roosevelt joked that perhaps 49,000 would do.
Churchill, believing them to be serious, denounced the idea of "the cold-blooded execution of soldiers who fought for their country" and that he would rather be "taken out in the courtyard and shot" himself than partake in any such action.
However, he also stated that war criminals must pay for their crimes and that, under the Moscow Document which he had written, they should be tried at the places where the crimes were committed.
Churchill was vigorously opposed to executions "for political purposes."
According to the minutes of a meeting between Roosevelt and Stalin at Yalta, on 4 February 1945, at the Livadia Palace, President Roosevelt "said that he had been very much struck by the extent of German destruction in Crimea and therefore he was more bloodthirsty in regard to the Germans than he had been a year ago, and he hoped that Marshal Stalin would again propose a toast to the execution of 50,000 officers of the German Army."

Henry Morgenthau Jr., US Secretary of the Treasury, suggested a plan for the total denazification of Germany; this was known as the Morgenthau Plan.
The plan advocated the forced de-industrialisation of Germany and the summary execution of so-called "arch-criminals", i.e. the major war criminals.
Roosevelt initially supported this plan, and managed to convince Churchill to support it in a less drastic form.
Later, details were leaked in the US generating widespread condemnation by the nation's newspapers and propaganda was published about the plan in Germany.
Roosevelt, aware of strong public disapproval, abandoned the plan, but did not adopt an alternative position on the matter.
The demise of the Morgenthau Plan created the need for an alternative method of dealing with the Nazi leadership.
The plan for the "Trial of European War Criminals"
A precedent for trying those accused of war crimes had been set at the end of World War I in the Leipzig War Crimes Trials held in May to July 1921 before the Reichsgericht (German Supreme Court) in Leipzig, although these had been on a very limited scale and largely regarded as ineffectual. At the beginning of 1940, the Polish government-in-exile asked the British and French governments to condemn the German invasion of their country. The British initially declined to do so; however, in April 1940, a joint declaration was issued by the British, French, and Polish. Relatively bland because of Anglo-French reservations, it proclaimed the trio's "desire to make a formal and public protest to the conscience of the world against the action of the German government whom they must hold responsible for these crimes which cannot remain unpunished."
Three-and-a-half years later, the stated intention to punish the Germans was much more trenchant. On 1 November 1943, the Soviet Union, the United Kingdom, and the United States published their "Declaration on German Atrocities in Occupied Europe", which gave a "full warning" that, when the Nazis were defeated, the Allies would "pursue them to the uttermost ends of the earth ... so that justice may be done. ... The above declaration is without prejudice to the case of the major war criminals whose offenses have no particular geographical location and who will be punished by a joint decision of the Government of the Allies." This intention by the Allies to dispense justice was reiterated at the Yalta Conference and at Potsdam in 1945.
British War Cabinet documents, released on 2 January 2006, showed that as early as December 1944 the Cabinet had discussed their policy for the punishment of the leading Nazis if captured. The British Prime Minister, Winston Churchill, had then advocated a policy of summary execution in some circumstances, with the use of an Act of Attainder to circumvent legal obstacles, being dissuaded from this only by talks with US and Soviet leaders later in the war.
In late 1943, during the Tripartite Dinner Meeting at the Tehran Conference, the Soviet leader, Joseph Stalin, proposed executing 50,000–100,000 German staff officers. US President Franklin D. Roosevelt joked that perhaps 49,000 would do. Churchill, believing them to be serious, denounced the idea of "the cold-blooded execution of soldiers who fought for their country" and that he would rather be "taken out in the courtyard and shot" himself than partake in any such action. However, he also stated that war criminals must pay for their crimes and that, under the Moscow Document which he had written, they should be tried at the places where the crimes were committed. Churchill was vigorously opposed to executions "for political purposes." According to the minutes of a meeting between Roosevelt and Stalin at Yalta, on 4 February 1945, at the Livadia Palace, President Roosevelt "said that he had been very much struck by the extent of German destruction in Crimea and therefore he was more bloodthirsty in regard to the Germans than he had been a year ago, and he hoped that Marshal Stalin would again propose a toast to the execution of 50,000 officers of the German Army."
Henry Morgenthau Jr., US Secretary of the Treasury, suggested a plan for the total denazification of Germany; this was known as the Morgenthau Plan. The plan advocated the forced de-industrialisation of Germany and the summary execution of so-called "arch-criminals", i.e. the major war criminals. Roosevelt initially supported this plan, and managed to convince Churchill to support it in a less drastic form. Later, details were leaked in the US generating widespread condemnation by the nation's newspapers and propaganda was published about the plan in Germany. Roosevelt, aware of strong public disapproval, abandoned the plan, but did not adopt an alternative position on the matter. The demise of the Morgenthau Plan created the need for an alternative method of dealing with the Nazi leadership. The plan for the "Trial of European War Criminals" 
Nuremberg trials