That is not true and was the original Domino Theory BS to justify the war that never should have been fought. Read the two books by Col. Fletcher Prouty and you will learn a lot of history about the war you never knew. Basically it was a CIA operation all the way.
You really think the Gulf of Tonkin incident was an accident?
The mistake was allowing France to get Indochina back after the war.
Totally planned just like what you’re seeing in Ukraine today. The big difference is the magnitude of the threat to the world. There is zero threat to the world from Russia today. In 1964 it was give and take whether we’d survive the Chinese, Soviets and Warsaw Pact monolithic assault upon the Free World. Yes, Free World actually meant something sixty years ago.