The cornerstone of the policy of containment came when George F. Kennan sent his "long telegram" from the U.S. embassy in Moscow in 1946. The document contained a clear message that the Soviet Union was inherently insecure and expansionist, and that ultimately Soviet leaders wanted to control their neighboring countries to shield themselves from traditional enemies. Ultimately, Kennan argued, the Soviets wanted to overthrow western governments.
The thesis laid out by Kennan took hold in Washington, where the Truman administration began to take a bolder stance against the Soviet Union. For example, he promised aid to all those countries who worked to resist communist influence.
The idea of containment, as Kennan argued later in his life, was eventually expanded beyond what he had argued. Kennan was a believer in diplomatic and political containment and pressure, not necessarily military containment. But when Eisenhower reached office, he began a huge build up of nuclear weapons, aimed squarely at containing the Soviet Union.
It was remarkable, at the time, how quickly after the war ended that the United States and the Soviet Union became locked in a cold war that would last for decades.
For one thing, the policy of "containment" was the main reason why the C.I.A. was created. The C.I.A. had from the start the mandate to get information or intervene in other countries' affairs without going public. In 1942 Rooservelt had established the OSS (Office of Secret Services), which in 1947 was restructured and redefined as The Central Intelligence Agency:
Frank Wisner (nominated head of the OSS) remained concerned about the spread of communism and began lobbying for a new intelligence agency...The Office of Special Projects was created in 1948. Soon afterwards it was renamed the Office of Policy Coordination (OPC). This became the espionage and counter-intelligence branch of the Central Intelligence Agency.
Wisner was told to create an organization that concentrated on "propaganda, economic warfare; preventive direct action, including sabotage, anti-sabotage, demolition and evacuation measures; subversion against hostile states, including assistance to underground resistance groups, and support of indigenous anti-Communist elements in threatened countries of the free world."
'Operation Mockingbird,' a program to sway public opinion via the media, was created later that year. Wisner took on Philip Graham of the Washington Post as head of this "mission."
"By the early 1950s, Wisner 'owned' respected members of the New York Times, Newsweek, CBS and other communications vehicles." (quote cited from Deborah Davis, journalist)