Answer:
Truman Doctrine.
The Truman Doctrine states that the United States would aid any European country that was fighting communism.
Step-by-step explanation:
The doctrine was born from a speech given by president Harry Truman on March 12, 1947 before Congress. It states that the US would provide economic, political and military aid to any country under the threat of domestic or foreign authoritarian forces (like Soviet communism). It was directly prompted by the British announcement Britain would stop providing aid to Greece in its fight against a communist insurgency.