In early 1971, The New York Times Book Review splashed its cover with the question “Should We Have War Crimes Trials?” American perceptions of the war in Vietnam were at a tipping point, and the military was nervous. A retired general and respected prosecutor at Nuremberg argued in The Times and on The Dick Cavett Show that Gen. William Westmoreland might be guilty of war crimes. “Our army that now remains in Vietnam,” a colonel wrote at the time, “is in a state approaching collapse, with individual units avoiding or having refused combat, murdering their officers . . . . drug-ridden, and dispirited where not near-mutinous.”

As Nick Turse tells it in his indispensable new history of the war, challenges to the military’s perceptions of the conflict, which it pretended to be winning every day for years, started with Seymour Hersh’s groundbreaking account of the My Lai massacre. American soldiers murdered 500 Vietnamese civilians at My Lai in 1968, and after Hersh’s expos, suddenly war crimes were a hot story. For a moment. But Turse insists that if the editors of Newsweek hadn’t “eviscerated” an article that described a much larger death toll in 1972, the wool wouldn’t still be pulled over Americans’ eyes.

The problem, as described in Kill Anything That Moves, is the tension between the “bad apples” argument — which sees atrocities in Vietnam as the exception — and the reality of the broader, official “American way of war.” Turse came to understand the latter after he stumbled onto documents of the Vietnam War Crimes Working Group. The military created the group after the My Lai massacre to avoid again being caught flat-footed.

The point, Turse found, was not to prevent war crimes but to contain the damage and stay ahead of the PR problem. Finding the cache of internal documents, Turse interviewed more than 100 veterans, alongside those of eyewitnesses and survivors of American atrocities in Vietnam. His verdict — more than a decade later — is damning and masterful.

Without knowing its name, Americans understand what a free-fire zone is. Presidents George W. Bush and Barack Obama have essentially made large swaths of Pakistan into them. As Turse recounts, the practice seems to have originated in Vietnam (though no doubt there are earlier precedents in the American wars against Indians).

A free-fire zone in Vietnam, as American soldiers understood it, was where all inhabitants were deemed to be the enemy. They could therefore be killed at will (or raped, mutilated, kidnapped, tortured, used to find and explode land mines). Arbitrarily, too: for running as American soldiers approached, for wearing black, for having safety shelters under their houses, for merely being — all Vietnamese in these zones were fair game.

The practice was so liberating of some soldiers’ latent sadism that, when questioned over the use of deadly force, some even insisted that nonofficial free-fire zones were free-fire zones. Likewise, obsession over the body count (in light of American racism and what soldiers called “the mere-gook rule”) also led to abuses. Turse finds in the documents that official policy held that if more “VC” could be killed than replaced, this would stand for “winning.” If you add to this the internal military survey of officers’ understanding of the Geneva Conventions, which found that more than 96 percent of Marine second lieutenants would torture at will to get information, then the “fog of war” comes into sharper focus.