What did Truman mean when he claimed," should we fail to aid Greece and Turkey in this fateful hour, the effect will be far reaching to the West as to the East"?

Truman was afraid that the two countries might become communist nations and that this type of ideology would spread to the rest of the surrounding countries. To stop this growth of communism Truman created the Truman doctrine which insured any country that was under the threat of communism would be aided by the United States no matter where they were.