What statement shows the most likely reason why people would view the Vietnam War as a US failure?

Democracy survived in Vietnam after the war

Communism spread when North Vietnam took over South Vietnam

Vietnam became one unified country with a constitution like the USâs

The Vietnam War would end up being a direct cause of the Korean War

Communism spread when North Vietnam took over South Vietnam

The statement that shows the most likely reason why people would view the Vietnam War as a US failure is that Communism spread when North Vietnam took over South Vietnam, as the war was justified first and foremost as a campaign to avoid the spread of Communism, thus when such spread did happen, the campaign was viewed as a failure.