The Vietnam War was a major military conflict that took place primarily between 1955 and 1975, pitting the communist government of North Vietnam against South Vietnam and its principal ally, the United States. It was one of the longest and most controversial wars in American history, deeply dividing the country at home while causing devastating loss of life across Southeast Asia. The war ended with a North Vietnamese victory and the reunification of Vietnam under communist rule, leaving a lasting impact on American foreign policy and society.