The Sunni militants who now threaten to take over Iraq seemed to spring from nowhere when they stormed Mosul in early June. But the group that recently renamed itself simply ‘the Islamic State” has existed under various names and in various shapes since the early 1990s. And its story is the story of how modern terrorism has evolved, from a political and religious ideal into a death-cult.

The group began over two decades ago as a fervid fantasy in the mind of a Jordanian named Abu Musab al-Zarqawi. A onetime street thug, he arrived in Afghanistan as a mujahideen wannabe in 1989, a year too late to fight the Soviet Union. He went back home to Jordan, and remained a fringe figure in the international violent ‘jihad” for much of the following decade. He returned to Afghanistan to set up a training camp for terrorists, and met Osama bin Laden in 1999, but chose not to join al-Qaeda.

The fall of the Taliban in 2001 forced Zarqawi to flee to Iraq. There his presence went largely unnoticed until the Bush administration used […]