George Frost Kennan was an American diplomat and historian who lived from February 16, 1904, to March 17, 2005. During the Cold War, he gained most notoriety as a supporter of the containment of Soviet expansion. In addition to writing academic histories of USSR-US ties, he gave several lectures. In addition, he belonged to the group of wise men in foreign policy known as "The Wise Men." His writings in the late 1940s served as the impetus for the US foreign strategy of limiting the USSR and the Truman Doctrine. His 1946 "Long Telegram" from Moscow and the paper "The Sources of Soviet Conduct" that followed made the case that the Soviet system was inevitably expansionist and that its influence needed to be "contained" in areas that were crucially important to US strategy. The new anti-Soviet strategy of the Truman administration was justified by these writings. Kennan was instrumental in the creation of key Cold War initiatives and organizations, most notably the Marshall Plan. Kennan started to critique the foreign policies that he had assisted in articulating not long after his ideas had become U.S. policy. Kennan started to feel optimistic about the US starting constructive talks with the Soviet leadership by the end of 1948.