Most historians of the Islamic State agree that the group emerged out of al-Qaeda in Iraq as a response to the U.S. invasion in 2003. They also agree that it was shaped primarily by a Jordanian jihadist and the eventual head of al-Qaeda in Iraq, Abu Musab al-Zarqawi. The Jordanian had a dark vision: He wished to fuel a civil war between Sunnis and Shiites and establish a caliphate. Although he was killed in 2006, his vision was realized in 2014—the year ISIS overran northern Iraq and eastern Syria.
Recently, I came to question the conventional wisdom. The groundwork for ISIS was arguably laid long before the invasion, and if there was one person responsible for the group’s modus operandi, it was Abdulrahman al-Qaduli, an Iraqi from Nineveh better known by his nom de guerre, Abu Ali al-Anbari—not Zarqawi. It was Anbari, Zarqawi’s No. 2 in his al-Qaeda years, who defined the Islamic State’s radical approach more than any other person; his influence was more systematic, longer lasting, and deeper than that of Zarqawi.