Truman's presidential style definitely contributed to the Cold War. He was much more outwardly aggressive in showing his dislike and distrust of the Soviets than Franklin Delano Roosevelt. Truman believed Roosevelt was too soft with Stalin and that he did not stand up to the Soviets as much as Truman believed the Americans/Western Powers should have. Truman's outburst shocked and angered the Soviets, which contributed to increasing tensions between the Soviets and the Americans. Truman did not really want to deal with the Soviets diplomatically, which was one of the reasons the Cold War began. Truman was not looking to make any negotiations or compromises with the Soviets. .
American expectations for the postwar world certainly contributed to the development of the Cold War. After the war, disputes between the Soviet Union and the American democracy (due to the Soviets not fulfilling America's expectations), particularly over the Soviet takeover of East European states, led Winston Churchill to warn in 1946 that an "iron curtain" was descending through the middle of Europe. American's expectations of the occupation policy in Germany also contributed to the Cold War. .
The United States dropping of the atomic bomb in Hiroshima and Nagasaki also undeniably contributed to the growth of the Cold War. American possession and use of nuclear weapons had spurred the Soviets to accelerate their own nuclear weapons development projects. Scientists knew that it was only a matter of time until the Soviets produce a bomb. Because the Soviets realized that the Americans possessed and used nuclear weapons, the Soviets felt compelled to have their very own nuclear weapons to defend their country. The world would then be at the mercy of a costly and dangerous arms race without precedent in human history. It became a competition "a highly heated competition "about who can make the greatest amount and most effective nuclear weapons.