Answer:
The domino theory was a Cold War policy that suggested a communist government in one nation would quickly lead to communist takeovers in neighboring states, each falling like a perfectly aligned row of dominos. China had become communist in 1949 and communists were in control of North Vietnam. The USA was afraid that communism would spread to South Vietnam and then the rest of Asia. It decided to send money, supplies, and military advisers to help South Vietnamese Government.
Step-by-step explanation: