Why Was the Vietnam War Waged

Why was the Vietnam War waged?

A) In part, the Vietnam War was waged because the United States thought that Japan would intercede on behalf of the Vietnamese.
B) In part, the Vietnam War was waged because the United States feared that Vietnam would join China in the communist camp.
C) In part, the Vietnam War was waged because the United States assumed that Vietnam would soon have access to nuclear weapons.
D) In part, the Vietnam War was waged because the United States suffered an attack on its embassy that was orchestrated by the Vietnamese.