In the lead-up to the Truman Doctrine.

The policy of containment was one of the most important policies the US developed. Not only did it suggest to actively seeking to prevent the spread of communism, but also it was also the key aim in "Truman Doctrine"--the Doctrine that veered the US's attitude towards the rest of the world. It said, "it was America's duty to interfere to 'help free peoples to work out their own destiny in their own way'", which …

…Doctrine," and the policy of containment officially formed. Nearly all the events that took place since 1917 contributed some tensions for US deciding to have the policy of containment, but the events that happened in 1945-1946 had more important roles to play for the policy of containment. The establishment of the policy of containment was another symbol of the declaration of the famous Cold War. 1 Clare, John. http://www.johndclare.net/Smartass_ColdWar.htm, Kennan. September 4, 2005.