In 1945, The Grand Alliance started to breakdown, as there was no common enemy to fight against anymore. Also, the western part of Europe didn't like the idea of Communism.
Stalin (Left), FDR (Middle), Churchill (Right)
America was capitalist, and Russia was communist, and they're relationship was strained because they believed in different things.
Communism is better! Everyone gets the same amount of earnings!
Capitalist is better! Everyone has freedom of speech!
Three people (George Kennan, Nikolai Novikov and Winston Churchill) all made speeches/telegrams about the iron curtain. Two of the people where from Capitalist countries and one of them was from a communist country. All of the telegrams/speeches caused tension to rise between America and Soviet Union.
America had two policies called the Truman Doctrine and the Marshall Plan. They were both to help countries in need, but it also tried to get them to be a capitalist country.
We (America) will give you money and supplies, but you might want to consider being a Capitalist country, for your sake.