After fighting the war in Korea, the US had learned that communism would spread. In order to keep with their policy of containment, they had to rush in and stop Viet Cong from spreading communism (much like the domino theory that the US had). Had Viet Cong not wanted to bring about communism, there would be no need for invasion, and the domino theory would have yet to be proven.
A tight money policy means "the Federal Reserve wants to decrease the <span>amount of money" in the economy, which is usually done by restricting credit and raising interest rates. </span>
