Question

vietnams war for independence and division into two countries in 1954 led the united states to send military forces to the region. why did this take place?
the united states wanted to establish colonies of its own.
the united states disagreed with the boundary that had been put in place.
the united states feared the spread of communism throughout southeast asia.
the united states wanted to keep the british from returning to southeast asia.

Explanation:

During the Cold War, the U.S. had a policy of containment. Vietnam's division (with the North being communist) made the U.S. fear the "domino theory" - that if one country fell to communism, others in the region would follow. So, they sent military forces to prevent the spread of communism in Southeast Asia.

Answer:

The United States feared the spread of Communism throughout Southeast Asia.