The Vietnam War was a long and divisive conflict between communist North Vietnam and its allies, and South Vietnam, supported by the United States.

The U.S. became involved based on the 'domino theory,' the fear that if one Southeast Asian country fell to communism, others would follow.

U.S. involvement escalated from sending military advisors in the 1950s to deploying hundreds of thousands of combat troops in the mid-1960s.

The war was characterized by guerrilla warfare conducted by the Viet Cong (communist insurgents in the South) and conventional fighting by the North Vietnamese Army.

The U.S. military used overwhelming firepower, including a massive bombing campaign, but struggled to defeat the elusive enemy.

The Tet Offensive of 1968 was a major turning point; although a military defeat for the communists, it shattered public confidence in the U.S. war effort.

The war became deeply unpopular in the United States, leading to a powerful anti-war movement.

President Richard Nixon implemented a policy of 'Vietnamization,' gradually withdrawing U.S. troops while supporting the South Vietnamese army.

The U.S. withdrew its last combat troops in 1973.

In 1975, North Vietnam launched a final offensive, capturing the South Vietnamese capital of Saigon and unifying the country under communist rule.