Vietnam's 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 became involved because its leaders feared that Communism would spread from Vietnam to other countries in Southeast Asia. This concern was known as the domino theory: if one country became Communist, nearby countries might follow. So the best answer is “The United States feared the spread of Communism throughout Southeast Asia.”

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