Several United States Presidents committed military troops to serve in Vietnam in an effort to

a. react to violations of United States neutrality.

b. support the policy of containment.

c. oppose the Chinese occupation of Indochina.

d. protect United States economic interests in East Asia.

The purpose of sending troops to Vietnam was to prevent Vietnam from becoming a communist state - much like the neighbouring China did. The US feared the domino effect in which more and more neighbouring states become communist.

This policy was called the containment policy (the answer is B) - communism were to be contained.