FRONTLINE investigates the miscalculations and mistakes behind the brutal rise of ISIS. Correspondent Martin Smith, who made "Truth, War & Consequences," "Beyond Baghdad," "Private Warriors" and "Gangs of Iraq," reports from Iraq on how the country began coming undone after the American withdrawal and what it means for the U.S. to be fighting there again.

Months into his second term, President Donald Trump welcomed Saudi Crown Prince Mohammed bin Salman to the White House. It had been seven years since a Saudi hit squad murdered journalist Jamal Khashoggi, in an operation U.S. intelligence assessed MBS had approved.Now, Trump hailed MBS as a friend. The two men announced from the Oval Office that Saudi Arabia planned to invest hundreds of billions of dollars in the U.S.FRONTLINE's new documentary "The Crown Prince & the President" draws on over 100 interviews to investigate what forces bind the two men and their countries together, and what each stands to gain.

In August 1998, two cars exploded simultaneously at U.S. embassies in Kenya and Tanzania, killing 268 and injuring 5,000. CIA and FBI investigators soon identified suspects, including accused mastermind and Saudi exile Osama bin Laden. But was this an individual terrorist act, or a symptom of deeply rooted anti-U.S. vendettas? In collaboration with The New York Times, "Frontline" investigates bin Laden, his followers, and the Africa bombings.