Soviet Union

The Sources of Soviet Conduct: The Essence of Kennan’s Article
The essence of George F. Kennan’s article “The Sources of Soviet Conduct” is that Soviet conduct is based on the ideology of the founders of the Soviet system in Russia and on the circumstances that Soviet rule has foisted upon the country. Kennan breaks down what that ideology is and what those circumstances are in his article. For Soviets, Moscow was infallible, as Kennan (1947) described: the state was the supreme arbiter of the direction that society should take and its ideology was such that it could never collaborate with the capitalistic West but must, inevitably, act as a force opposed to the pursuits of the West. The essence of the Soviet State, according to Kennan, was that it would bide its time until the capitalist West collapsed under the weight of its own internal corruption. At that time, the Soviets would facilitate the revolution of the working class. Till then, the Soviet State was perfectly willing to wait and put forward a friendly face.
The Truman Administration embraced the concept because Truman wanted to appear strong. That is why he dropped to nuclear bombs on Japan to end WWII. He wanted to demonstrate with a show of force the fact that he was willing to and capable of causing massive destruction. It was a message to the Soviet Union: if you oppose us, we will not only win but we will utterly destroy you. The Truman Administration embraced the idea that the Soviet Union was ultimately opposed to the U.S. because the U.S. was ultimately opposed to the Soviet Union, at least under Truman. Roosevelt had been more inclined to work with the Soviets. Kennedy, at times, expressed a more hopeful attitude towards the Soviets. Truman was set on stopping the advance of the Communist ideology and he wanted no push back from the Soviets.
References
Kennan, George F. “The Sources of Soviet Conduct” by X. Foreign Affairs (July 1947): 566–82.