In 1945, after the end of World War II, the United States moved away from isolationism and became active throughout the world.
THE TRUMAN DOCTRINE AND MARSHAL PLANIQBAL 11 SOC
There was an economic crisis in Eastern Europe as they struggled to rebuild after the War, as well as food shortages, unemployment, and millions of refuges moving towards the West. Communist parties in France and Italy were gaining support.
Meanwhile, the Soviet Union continued to spread communism through Eastern Europe. In 1946, Cold War attitudes develop as Soviet troops march into Persia, before withdrawing after a US intervention at the United Nations.
After a plea for help from Britain, Truman announced that America would financially help and support any country willing to stop the spread of communism on March 1947, calling it the Truman Doctrine.
The United States creates a new policy called the Marshall Plan in 1947, offering massive economic aid to Western Europe. It succeeded in bringing over $13000 million over four years in aid. The plan ended in 1952.
The Soviet Union saw the aid as the US trying to spread its capitalist ideals. They create COMINFORM and COMECOM in September 1947 as an alternative for communist countries to fight the Marshall plan. It was not as successful.