Why did you go to war at Vietnam?
To fight communism.
There was no "Vietnam" during the Vietnam War. Communist NORTH Vietnam was attacking non-communist SOUTH Vietnam, and the US was trying to drive the communists out of South Vietnam...trying to stop communist aggression. It's called the Vietnam War because it's a lot easier to say, and less confusing...than to say "South Vietnam War" or "North Vietnam War", so some people go so far as to say the war in Southeast Asia instead.
The Tonkin Gulf Resolution: It commenced open warfare between the United States and North Vietnam. Prior to the TG Resolution there was only war in South Vietnam; it was a guerrilla war and did not openly involve North Vietnam...nor was North Vietnam openly bombed by US aircraft. No, Ike did (Eisenhower).