Pulitzer Prize-winning reporter Joby Warrick reveals how the strain of militant Islam now raising its banner across Iraq and Syria spread from a remote Jordanian prison with the unwitting aid of American military intervention.

When he succeeded his father in 1999, King Abdullah of Jordan released a batch of political prisoners in the hopes of smoothing his transition to power. Little did he know that among those released was Abu Musab al-Zarqawi, a man who would go on to become a terrorist mastermind too dangerous even for al-Qaeda and give rise to an Islamist movement bent on dominating the Middle East.

Zarqawi began by directing hotel bombings and assassinations in Jordan from a base in northern Iraq, but it was the American invasion of that country in 2003 that catapulted him to the head of a vast insurgency. By identifying him as the link between Saddam and bin Laden, the CIA inadvertently created a monster. Like-minded radicals saw him as a hero resisting the infidel occupiers and rallied to his cause. Their wave of brutal beheadings and suicide bombings continued for years until Jordanian intelligence provided the Americans with the crucial intelligence needed to eliminate Zarqawi in a 2006 airstrike.

But his movement endured, first called al-Qaeda in Iraq, then renamed Islamic State of Iraq and Syria, or ISIS, seeking refuge in unstable, ungoverned pockets on the Iraq-Syria border. And as the Syrian civil war broke out in 2011, ISIS seized its chance to pursue Zarqawi's dream of a sweeping, ultra-conservative Islamic caliphate.

Drawing on unique access to CIA and Jordanian sources, Joby Warrick weaves together heart-pounding, moment-by-moment operational details with overarching historical perspectives to reveal the long trajectory of today's most dangerous Islamic extremist threat.