Final answer:
Option (2), The United States withdrew its military forces from Vietnam after reaching a cease-fire in 1973, without defeating the Vietnamese communists.
Step-by-step explanation:
The United States military forces did not withdraw from Vietnam after defeating Vietnamese communists; rather, they withdrew after a cease-fire agreement was reached in 1973. The war did not end with this withdrawal, as the fighting continued until 1975, when the North Vietnamese communists overran South Vietnam, leading to the reunification of Vietnam under a communist government.
This outcome was a stark contrast to the initial objective of the American military presence in South Vietnam, which was to prevent the spread of communism. The Vietnam War had significant impacts, including the loss of over 57,000 US soldiers and over a million Vietnamese lives.