Mayer's opinion is that the greatest failure of the Treaty of Versailles was that it was a triumph for the "Old Diplomacy" with only minor elements of "New Diplomacy". According to Mayer, the irrational fears generated by the Russian Revolution resulted in an international system designed to contain the Soviet Union. A major influence on Mayer was the British historian E. H. Carr, who was his friend and mentor. In 1961, Mayer played a major role in the American publication of Carr's book "What Is History?" Many of Mayer's writings concerning international affairs during the interwar era use the assumptions of Carr's 1939 book "The Twenty Year's Crisis".