The end of World War I saw the United States retreat into isolation. The Senate refused to ratify the Versailles Peace Treaty that ended World War I. The U.S. failed to join the League of Nations--the international organization that was the less-successful interwar predecessor of the United Nations. The U.S. raised tariffs early in the 1920s (although not to levels that appreciably discouraged imports). Most important, perhaps, the 1920s saw the end of free immigration into the United States. Migration from Asia had been restricted for several generations. Migration from Africa had never b…
