Washington was at war with Hanoi.
North Korea & North Vietnam.
US presidents consistently used the words, "stopping Communist aggression" during their speeches.
about 1957
The allies during the Vietnam War were the US, South Viets, South Koreans, Thai's, Philippines, Australia and New Zealanders.
The USAF & USN fought in NORTH Vietnam (in the skies); the US Army & USMC fought on the ground in SOUTH Vietnam.
Because of US Policy to fight communism.
To fight communism.
The US fought for the South.
North Vietnam (capital was Hanoi).
South Vietnam was considered an ally of the US.
To prevent the communist take over of the Republic of South Vietnam.