You can see the ideas about Tension between the two superpowers in an article here.
The idea is that USA and USSR had completely different ideologies, with USA believing in Capitalism and USSR believing in Communism from Karl Marx. Capitalism and Communism don’t work with each other, which is why they were called the “The Strange Alliance.” Not only that, but they had major conflicts in the Russian Civil War, with the Bolsheviks succeeding in the war. Also during the First World War, Russia had retreated first, which caused suspicions for the USA, creating this tension.
The only thing that bought them together was the idea of “Alliance of Necessity” which helped them have one common idea: to get rid of Hitler.
However, that common idea alone was insufficient to help them work together, as Stalin intended to spread Communism for security. There were some strains upon the alliance, which had negative effects of suspicions being created for both Superpowers. E.g. the issues of Poland before World War 2. Britain knew that, due to Poland’s geographical location, it was paramount for the Soviet Union’s security. However, there were problems with the USSR and Poland, as USSR was believed to be responsible for the death of 10,000 Polish officers, when it was actually the Nazi Germans that invaded Poland.
Another factor that caused suspicion for Stalin was the timing of the Second Front. Stalin proposed to open up a Second Front against Germany due to how many soldiers, the material and human resources he has lost whilst fighting against Germany. However, USA and Britain refused to do so, which led Stalin to think that USA and Britain would let Hitler invade the Soviet Union again before they counter attack. This opened up suspicion upon his allies, but did not have proof whether USA and Britain would betray him.
That concludes how the Superpowers increased their tension. Truman, Vice President of USA, believed that Roosevelt was too soft to Stalin, as he wasn’t a strong Anti-communist. From then on, USSR continued to spread ideas of Communism to neighboring countries for this desperate notion of security to prevent future raids against the Soviet Union. This would naturally anger the USA, as both ideologies would not work together, which further increased the tension between these two superpowers, soon developing into a Cold War.