Perceptions and misperceptions were very important causes of the Cold War. For one, Stalin broke promises he made to the Allies after World War II, creating an atmosphere of suspicion and mistrust. Secondly, Stalin blatantly created the Iron Curtain in an attempt to protect the Eastern Bloc from the capitalist west, creating tension. Lastly, the construction of the North Atlantic Treaty Organization (NATO), along with the Warsaw Pact, made it clear that America and the Soviet Union were on the brink of war.
When Churchill, Roosevelt, and Stalin met at Yalta to discuss the fate of post–World War II Germany, Stalin promised to let democracy flourish in eastern Europe. He vowed not to spread communism. From the get-go, Britain was leery of Stalin and did not trust him. After all, he had originally been friendly with Nazi Germany before Hitler broke the pair's nonaggression pact. While Churchill did not believe a word Stalin said, Roosevelt decided to give him the benefit of the doubt. The American president said,
I just have a hunch that Stalin is not that kind of a man. . . . I think that if I give him everything I possibly can and ask for nothing from him in return, "noblesse oblige," he won't try to annex anything and will work with me for a world of democracy and peace.
However, once Roosevelt died and Truman became president, it became clear that Roosevelt's perception of Stalin may have been too rosy.
Truman was suspicious of communism in general. When Churchill, Truman, and Stalin met at Potsdam later that year, it was clear to Truman that Stalin had been lying about his intentions to not spread communism. Stalin had already begun aggressive expansion in eastern Europe, building his Eastern Bloc composed of satellite states to serve as a protective buffer between the communist east and the capitalist west. This division would come to be known as the Iron Curtain, a phrase that Churchill coined in his famous "Iron Curtain" speech.
Interestingly, even though Truman thought Stalin to be an untrustworthy leader, he made sure to mention to him at Potsdam that the United States was constructing a new, powerful weapon—the atomic bomb. However, because of Soviet spying, Stalin already knew of the bomb's existence. As tensions mounted between the two world superpowers, their perceptions and misperceptions of one another continued to fuel their militarism and want for protective alliances.
In 1949, the capitalist nations of the West decided to form a protective alliance against the communist east known NATO. As soon as the Soviets found out about this preemptive alliance, they became paranoid. Stalin worried that the alliance was planning to attack the Soviet Union and founded a rival alliance known as the Warsaw Pact in 1955. Almost every European nation was aligned with one of these two alliances, increasing tensions and creating a definite perception of that the two superpowers were going toe to toe. This brinksmanship would become a cornerstone of the Cold War and the many proxy wars of the era.