Why did the united states get involved vietnam conflict?

a. to make money for welfare programs.
b. to stop the spread of drugs.
c. to teach vietnamese children about democracy
d. to fight the spread of communism.

D) To fight the spread of communism.

Because of the Domino Theory they thought that if Vietnam fell into Communism, the whole region would follow. So therefore they wanted to support South Vietnam in order to contain Communism in Asia.

The answer is:

D.(To fight the spread of communism)

The U.S. entered the Vietnam War in an attempt to prevent the spread of communism, but foreign policy, economic interests, national fears, and geopolitical strategies also played major roles.

Hope this helps!

the answer to your question is:

strong-mayor system