This section covers Kelsen's years during his American years. Kelsen's participation and his part in the establishment of war crimes tribunals following WWII has been discussed in the previous section. The end of WWII and the start of the United Nations became a significant concern for Kelsen after 1940. For Kelsen, in principle, the United Nations represented in potential a significant phase change from the previous League of Nations and its numerous inadequacies which he had documented in his previous writings. Kelsen would write his 700-page treatise on the United Nations, along with a subsequent two hundred page supplement,