https://en.wikipedia.org/wiki/Vietnam_War_casualties#Deaths_caused_by_the_American_military

For official U.S. military operations reports, there was no established distinction between enemy KIA and civilian KIA. Since body counts were a direct measure of operational success, U.S. "operations reports" often listed civilian deaths as enemy KIA or exaggerated the number. There was strong pressure to produce body counts as a measure of operational success and enemy body counts were directly tied to promotions and commendation.[36][37][38][39] The My Lai massacre was initially written off as an operational success and covered up.[40][37] Sometimes civilian casualties from airstrikes or artillery barrages against villages were reported as "enemies killed".[36][37][41] All individuals killed in declared free-fire zones, combatants or not, were considered enemy killed in action by U.S. forces.[42] This might partially explain the discrepancies between recovered weapons and body-count figures, along with exaggeration, although the NVA and VC also went to great lengths to recover weapons from the battlefield.[14]

Nick Turse, in his 2013 book, Kill Anything that Moves, argues that a relentless drive toward higher body counts, a widespread use of free-fire zones, rules of engagement where civilians who ran from soldiers or helicopters could be viewed as VC, and a widespread disdain for Vietnamese civilians led to massive civilian casualties and endemic atrocities inflicted by U.S. troops.[45] One example cited by Turse is Operation Speedy Express, an operation by the 9th Infantry Division, which was described by John Paul Vann as, in effect, "many My Lais".[45]

Air force captain, Brian Wilson, who carried out bomb-damage assessments in free-fire zones throughout the delta, saw the results firsthand. "It was the epitome of immorality...One of the times I counted bodies after an air strike—which always ended with two napalm bombs which would just fry everything that was left—I counted sixty-two bodies. In my report I described them as so many women between fifteen and twenty-five and so many children—usually in their mothers' arms or very close to them—and so many old people." When he later read the official tally of dead, he found that it listed them as 130 VC killed.[46]

Indochina Newsletter, Issue 18, November – December, 1982, pp. 1-5 [October, 1982] - The Legacy of the Vietnam War

CHOMSKY: As far as the opinion makers are concerned, they have been doing exactly what it was obvious they would do. Every book that comes out, every article that comes out, talks about how — while it may have been a “mistake” or an “unwise effort” — the United States was defending South Vietnam from North Vietnamese aggression. And they portray those who opposed the war as apologists for North Vietnam. That’s standard to say.

The purpose is obvious: to obscure the fact that the United States did attack South Vietnam and the major war was fought against South Vietnam. The real invasion of South Vietnam which was directed largely against the rural society began directly in 1962 after many years of working through mercenaries and client groups. And that fact simply does not exist in official American history. There is no such event in American history as the attack on South Vietnam. That’s gone. Of course, It is a part of real history. But it’s not a part of official history.

...

QUESTION: This question of who the United States was fighting in Vietnam is pretty basic in terms of coming to any understanding of the war. But why would the U.S. attack South Vietnam, if the problem was not an attack from North Vietnam?

...

Then the National Liberation Front of South Vietnam was formed. And its founding program called for the neutralization of South Vietnam, Laos and Cambodia. And it’s very striking that the National Liberation Front was the only group that ever called for the independence of South Vietnam. The so-called South Vietnamese government (GVN) did not, but rather, claimed to be the government of all Vietnam. The National Liberation Front was the only South Vietnamese group that ever talked about South Vietnamese independence. They called for the neutralization of South Vietnam, Laos and Cambodia as a kind of neutral block, working toward some type of integration of the South with North Vietnam ultimately.

Now that proposal in 1962 caused panic in American ruling circles. From 1962 to 1965 the US was dedicated to try to prevent the independence of South Vietnam, the reason was of course that Kennedy and Johnson knew that if any political solution was permitted in the south, the National Liberation Front would effectively come to power, so strong was its political support in comparison with the political support of the so-called South Vietnamese government.

...

Well, why did they do it? Why was the United States so afraid of an independent South Vietnam? Well, I think the reason again is pretty clear from the internal government documents. Precisely what they were afraid of was that the “takeover” of South Vietnam by nationalist forces would not be brutal. They feared it would be conciliatory and that there would be successful social and economic development — and that the whole region might work.

This was clearly a nationalist movement — and in fact a radical nationalist movement which would separate Vietnam from the American orbit. It would not allow Vietnam to become another Philippines. It would trade with the United States but it would not be an American semi-colony.

https://www.encyclopedia.com/history/encyclopedias-almanacs-transcripts-and-maps/wars-effect-vietnamese-land-and-people

Despite the fact that South Vietnam was America's ally in the Vietnam War, it suffered severe damage to its land, people, and culture. The war also affected North Vietnam, but not as severely or as permanently as the South.