The USA’s involvement in Vietnam began in around 1944. Some timelines
1944-45. OAS supports Ho Chi Minh and the Viet Minh against the Japanese occupiers of Vietnam.
1945-1954.USA supports French return to Vietnam spending $4 billion helping the French and offering tactical nuclear weapons when it is clear that the French will lose at Dien Bien Phu.The French have the good sense to refuse the offer.
1954 USA and others including China decide on partition of Vietnam; agree on elections to reunify Vietnam to be held in
1956.USA organises through CIA a scare campaign about communists running northern Vietnam, and the communists were certainly extreme in their behaviour towards anyone with any wealth (a good few had been persecuted and shot by 1956 and their children and grandchildren black-listed), leading to mass exodus of tens of thousands to south of the 17th parallel. USA supports retention of Catholic Diem government in southern Vietnam contrary to 1954 Geneva agreement and starts sponsorship of sabotage in northern Vietnam.
1956-1964. USA sends in advisors totalling around 22 000 by 1964, if I recall correctly, in support of southern Vietnam government’s military efforts against infiltrating Viet Cong from northern Vietnam.
1964 USS Maddox, a destroyer, returning from picking up southern Vietnamese commandos who had been raiding something in northern Vietnam, is chased by north Vietnamese patrol boats when in Vietnamese territorial waters. Allegedy shots were fired from the patrol boats. This was the Gulf of Tonkin incident. USA Congress votes to start bombing northern Vietnam, which continued through to 1975 and also affected Laos and Cambodia.
Again, completely misjudged foreign policy. The OAS operative in 1944-45 was recommending collaboration with Ho Chi Minh. The historical imperative of Vietnam has always been to keep the Chinese out of the country, as evident from 2000 years plus of Vietnamese history. The USA had in 1945 a golden opportunity to support Ho Chi Minh to rebuild Vietnam as an allay; the Chinese were seen (and still are seen in Vietnam) as a threat worse than either the French or the USA.
The White House and Pentagon have a long history of simply not being able to “do Empire” properly. Bombing people is the mark of incompetence and failure. The Chinese are winning.