How did the united states begin to send aid to nations fighting communism?

The United States sent money and military aid to several different countries fighting communism.

A perfect example of this would be the Truman Doctrine. This gave $400 million to the countries of Turkey and Greece. Along with this, the US also gave $13 billion to countries like Great Britain, France, and Denmark through the Marshall Plan.

Besides money, the US sent troops to support countries fighting communism. This was true for both the Korean and Vietnam War, as the US sent troops to South Korea and South Vietnam to help them in their fight against communism.