The USA and USSR became rivals in summer 1945 because of many reasons. One of the reasons was that the USA was a capitalist country, a culture where anyone could be rich if they worked hard enough. However in USSR they operated under communism. Both nations had fears of the other nation imposing their own system of government upon the world. These fears were highlighted when Stalin attempted to get as much territory for the USSR and communism as he could. The USA thought this was Stalin’s attempt to turn the world ‘Red’
There were already bad feelings betwixt the two nations from WW2. USSR accused the USA of delaying their attack upon the west side of Germany so that the Nazis and USSR forces would be depleted and the USA could sweep in avoiding possible casualties. This aggravated the Soviets a lot; they lost 20 million people in the war whereas USA only lost 400,000 troops. These feelings were highlighted and exposed when the two leaders had to converse and make decisions upon post WW2 issues. These underlying feelings definitely influenced how they treated each other.
The two countries were also at loggerheads to become the biggest force in Europe. The USA had acquired the atomic bomb but the Soviets had a massive army. This caused permanent suspicion between the nations, to see who would take the first steps to war.
The two countries also disagreed upon how to deal with Germany. Both understood they needed to learn from the mistakes of the Treaty of Versailles but yet again they both had completely different ideas. USSR wanted to completely cripple Germany, however USA wanted to help Germany and turn it into a proper running country that could be treated as allies. This caused further controversy and deepened the distaste between the nations.