Learning the hijackers benefitted from gaps in US intelligence, the White House justifies a secret surveillance program and "enhanced interrogation."

After two decades, the US aims to end its longest-ever war, but its withdrawal threatens to plunge Afghanistan back into repressive, bloody violence.

With no cohesive strategy, the war in Afghanistan squanders early successes and backfires, fueling disillusionment, corruption and a Taliban resurgence.

Survivors recount the horrors they endured on 9/11. Immediately after the attacks, George W. Bush begins charting America's aggressive military response.

Interviews and chilling archival recordings chronicle the chaos that unfolded during the 9/11 attacks, whose origins can be traced to the 1980s.