Roosevelt had been a strong supporter of the League of Nations back in 1919-20 , but was determined to avoid the mistakes Wilson had made . The United Nations was FDR 's highest postwar priority . He insisted on full coordination with the Republican leadership . He made sure that leading Republicans were on board , especially Senators Arthur Vandenberg of Michigan , and Warren Austin of Vermont . . In a broad sense , Roosevelt believed that the UN could solve the minor problems and provide the chief mechanism to resolve any major Issues that arose among the great powers , all of whom had a veto . For FDR creating the UN was the most important goal for the entire war effort . For FDR , " establishing the United nations organization was the overarching strategic goal , the absolute first priority . " Roosevelt was especially interested in international protection of human right , and in this area his wife played a major role as well . The Allies had agreed to the basic structure of the new body at the Dumbarton Oaks Conference in 1944 . At Yalta , Roosevelt , Churchill , and Stalin agreed to the establishment of the United Nations , as well as the structure of the United Nations Security Council . Stalin insisted on having a veto and FDR finally agreed . The participants at Yalta also agreed that the United Nations would convene for the first time in San Francisco in April 1945 in the United Nations Conference on International Organization . Roosevelt considered the United Nations to be his most important legacy . He provided continuous backstage political support at home and with Churchill and Stalin abroad . The Big Four of the United States , Britain , Soviet Union and China would make the major decisions , with France added later to provide permanent members of the all-powerful Security Council . Each had a veto power , thus avoiding the fatal weakness of the League of Nations , which had theoretically been able to order its members to act in defiance of their own parliaments
United Nations Conference on International Organization
United Nations Conference on International Organization
Foreign policy of the Franklin D. Roosevelt administration