In the interviews, more than 400 insiders offered unrestrained criticism of what went wrong in Afghanistan and how the United States became mired in nearly two decades of warfare.

With a bluntness rarely expressed in public, the interviews lay bare pent-up complaints, frustrations and confessions, along with second-guessing and backbiting.

“We were devoid of a fundamental understanding of Afghanistan — we didn’t know what we were doing,” Douglas Lute, a three-star Army general who served as the White House’s Afghan war czar during the Bush and Obama administrations, told government interviewers in 2015. He added: “What are we trying to do here? We didn’t have the foggiest notion of what we were undertaking.”

“If the American people knew the magnitude of this dysfunction . . . 2,400 lives lost,” Lute added, blaming the deaths of U.S. military personnel on bureaucratic breakdowns among Congress, the Pentagon and the State Department. “Who will say this was in vain?”

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