WWII Leading into the Cold War
By the end of WWII, the United States of America was considered as the hero of the war. The USA was credited with defeating both Germany and Japan. This lead to tension between the USSR and the USA because they had the most total and combat deaths in WWII by far. The USSR had a total death toll of around 15 million while the USA had a total death toll of around 400,000. Though the USSR had taken the heaviest hit, they are hardly credited for their immense contributions to the war effort.
Further Tension
The tension between the USA and the USSR continued to grow when the big three, Truman, Churchill, and Stalin, meet to divide up the defeated Germany.