George Frost Kennan was an American adviser, diplomat, political scientist, and historian, best known as "the father of containment" and as a key figure in the emergence of the Cold War. He later wrote standard histories of the relations between Russia and the Western powers. He was also a core member of the group of foreign policy elders known as "The Wise Men".
In the late 1940s, his writings inspired the Truman Doctrine and the U.S. foreign policy of "containing" the Soviet Union, thrusting him into a lifelong role as a leading authority on the Cold War. His "Long Telegram" from Moscow in 1946 and the subsequent 1947 article "The Sources of Soviet Conduct" argued that the Soviet regime was inherently expansionist and that its influence had to be "contained" in areas of vital strategic importance to the United States. These texts quickly emerged as foundation texts of the Cold War, expressing the Truman administration's new anti-Soviet Union policy. Kennan also played a leading role in the development of definitive Cold War programs and institutions, notably the Marshall Plan.
Soon after his concepts had become U.S. policy, Kennan began to criticize the foreign policies that he had seemingly helped launch. Subsequently, prior to the end of 1948, Kennan was confident the state of affairs in Western Europe had developed to the point where positive dialogue could commence with the Soviet Union. His proposals were discounted by the Truman administration and Kennan's influence was marginalized, particularly after Dean Acheson was appointed secretary of state in 1949. Soon thereafter, U.S. Cold War strategy assumed a more assertive and militaristic quality, causing Kennan to lament over what he believed was as an aberration of his previous assessments.
If you want to understand your government, don't begin by reading the Constitution. (It conveys precious little of the flavor of today's statecraft.) Instead, read selected portions of the Washington telephone directory containing listings for all the organizations with titles beginning with the word National.