For 18 years, America has been at war in Afghanistan. As part of a government project to understand what went wrong, a federal agency interviewed more than 400 people who had a direct role in the conflict. In those interviews, generals, ambassadors, diplomats and other insiders offered firsthand accounts of the mistakes that have prolonged the war.

The full, unsparing remarks and the identities of many of those who made them have never been made public — until now. After a three-year legal battle, The Washington Post won release of more than 2,000 pages of “Lessons Learned” interviews conducted by the Office of the Special Inspector General for Afghanistan Reconstruction. Those interviews reveal there was no consensus on the war’s objectives, let alone how to end the conflict.

To augment the previously undisclosed interviews, The Post also obtained hundreds of confidential memos by former defense secretary Donald H. Rumsfeld from the National Security Archive, a nonprofit research institute. Known as “snowflakes,” the memos are brief instructions or comments that the Pentagon leader dictated to his underlings as the war unfolded.

Together, the interviews and the Rumsfeld memos reveal a secret, unvarnished history of the conflict and offer new insights into how three presidential administrations have failed for nearly two decades to deliver on their promises to end the war.