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.

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Since 2001, more than 775,000 U.S. troops have deployed to Afghanistan, many repeatedly. Of those, 2,300 died there and 20,589 were wounded in action, according to Defense Department figures.

The interviews, through an extensive array of voices, bring into sharp relief the core failings of the war that persist to this day. They underscore how three presidents — George W. Bush, Barack Obama and Donald Trump — and their military commanders have been unable to deliver on their promises to prevail in Afghanistan.

With most speaking on the assumption that their remarks would not become public, U.S. officials acknowledged that their warfighting strategies were fatally flawed and that Washington wasted enormous sums of money trying to remake Afghanistan into a modern nation.