Perhaps the gravest threat to the rule of law came during the twentieth century, and in an international context, when brutal totalitarian regimes, in particular Hitler's and Stalin's, passed unconscionable laws, subverted legal safeguards, corrupted the independence of the judiciary, and instigated show trials. The law was made subject to naked evil. After the horrors of the Second World War, swift and brutal revenge could have been exacted on the beaten foe, Nazi Germany, especially by its equally vicious adversary, Soviet Russia. Churchill himself initially expressed a preference for summary execution with the use of an Act of Attainder to circumvent legal obstacles. Instead, post-war Europe oversaw two remarkable developments. The first was the creation, very much along common law principles, of the Nuremberg Tribunal to try the Nazi war criminals. The second was the drawing up of the European Convention on Human Rights, again largely devised by common law lawyers, led by Britain's main prosecutor at Nuremberg.

The trial of the major war criminals, held between 20 November 1945 and 1 October 1946 at Nuremberg, the cradle of Nazism, was unique. For the first time the surviving leaders of a defeated nation were put on trial for Criminal Conspiracy (Count 1), with specific counts alleging Crimes against Peace (Count 2), War Crimes (Count 3), and Crimes against Humanity (Count 4).