ISIS: Inside the Army of Terror by Michael Weiss and Hassan Hassan Regan Arts, 270 pp., $14.00 (paper) ISIS: The State of Terror by Jessica Stern and J.M. Berger Ecco, 385 pp., $27.99

The author has wide experience in the Middle East and was formerly an official of a NATO country. We respect the writer’s reasons for anonymity.

—The Editors

Ahmad Fadhil was eighteen when his father died in 1984. Photographs suggest that he was relatively short, chubby, and wore large glasses. He wasn’t a particularly poor student—he received a B grade in junior high—but he decided to leave school. There was work in the garment and leather factories in his home city of Zarqa, Jordan, but he chose instead to work in a video store, and earned enough money to pay for some tattoos. He also drank alcohol, took drugs, and got into trouble with the police. So his mother sent him to an Islamic self-help class. This sobered him up and put him on a different path. By the time Ahmad Fadhil died in 2006 he had laid the foundations of an independent Islamic state of eight million people that controlled a territory larger than Jordan itself.

The rise of Ahmad Fadhil—or as he was later known in the jihad, Abu Musab al-Zarqawi—and ISIS, the movement of which he was the founder, remains almost inexplicable. The year 2003, in which he began his operations in Iraq, seemed to many part of a mundane and unheroic age of Internet start-ups and a slowly expanding system of global trade. Despite the US-led invasion of Iraq that year, the borders of Syria and Iraq were stable. Secular Arab nationalism appeared to have triumphed over the older forces of tribe and religion. Different religious communities—Yezidis, Shabaks, Christians, Kaka’is, Shias, and Sunnis—continued to live alongside one another, as they had for a millennium or more. Iraqis and Syrians had better incomes, education, health systems, and infrastructure, and an apparently more positive future, than most citizens of the developing world. Who then could have imagined that a movement founded by a man from a video store in provincial Jordan would tear off a third of the territory of Syria and Iraq, shatter all these historical institutions, and—defeating the combined militaries of a dozen of the wealthiest countries on earth—create a mini empire?

The story is relatively easy to narrate, but much more difficult to understand. It begins in 1989, when Zarqawi, inspired by his Islamic self-help class, traveled from Jordan to “do jihad” in Afghanistan. Over the next decade he fought in the Afghan civil war, organized terrorist attacks in Jordan, spent years in a Jordanian jail, and returned—with al-Qaeda help—to set up a training camp in Herat in western Afghanistan. He was driven out of Afghanistan by the US-led invasion of 2001, but helped back onto his feet by the…