MOSUL, Iraq — Weeks after the militants seized the city, as fighters roamed the streets and religious extremists rewrote the laws, an order rang out from the loudspeakers of local mosques.
Public servants, the speakers blared, were to report to their former offices.
To make sure every government worker got the message, the militants followed up with phone calls to supervisors.
The phone call reached Muhammad Nasser Hamoud, a 19-year-veteran of the Iraqi Directorate of Agriculture, behind the locked gate of his home, where he was hiding with his family. Terrified but unsure what else to do, he and his colleagues trudged back to their six-story office complex decorated with posters of seed hybrids.
They arrived to find chairs lined up in neat rows.
The commander who strode in sat facing the room, his leg splayed out so that everyone could see the pistol holstered to his thigh. For a moment, the only sounds were the hurried prayers of the civil servants mumbling under their breath.
Their fears proved unfounded. The commander had a surprisingly tame request: Resume your jobs immediately. A sign-in sheet would be placed at the entrance to each department. Those who failed to show up would be punished.
Meetings like this one occurred throughout the territory controlled by the Islamic State group, also known as ISIS, in 2014. Soon municipal employees were back fixing potholes, painting crosswalks, repairing power lines, and overseeing payroll.
“We had no choice but to go back to work,’’ said Hamoud. “We did the same job as before. Except we were now serving a terrorist group.’’
The disheveled fighters who burst out of the desert more than three years ago founded a state that was acknowledged by no one except themselves. And yet for nearly three years, the Islamic State controlled a stretch of land that at one point was the size of Britain, with a population estimated at 12 million people. At its peak, it included a 100-mile coastline in Libya, a section of Nigeria’s lawless forests, and a city in the Philippines, as well as colonies in at least 13 other countries. By far the largest city under their rule was Mosul.
Nearly all of that territory has now been lost, but what the militants left behind helps answer the troubling question of their longevity: How did a group whose spectacles of violence galvanized the world against it hold onto so much land for so long?
Part of the answer can be found in more than 15,000 pages of Islamic State documents I recovered during five trips to Iraq over more than a year.
The Islamic State built a state of administrative efficiency that collected taxes and picked up the garbage. It ran a marriage office that oversaw medical examinations to ensure that couples could have children. It issued birth certificates — printed on Islamic State stationery — to babies born under the caliphate’s black flag. It even ran its own department of motor vehicles.
The documents and interviews with dozens of people who lived under their rule show that the group at times offered better services and proved itself more capable than the government it had replaced.
They also suggest that the militants learned from mistakes the United States made in 2003 after it invaded Iraq, including the decision to purge members of Saddam Hussein’s ruling party from their positions and bar them from future employment. That decree succeeded in erasing the Ba’athist state, but also gutted the country’s civil institutions, creating the power vacuum that groups like the Islamic State rushed to fill.
A little more than a decade later, after seizing huge tracts of Iraq and Syria, the militants tried a different tactic. They built their state on the back of the one that existed before, absorbing the administrative know-how of its hundreds of government cadres. An examination of how the group governed reveals a pattern of collaboration between the militants and the civilians under their yoke.
One of the keys to their success was their diversified revenue stream. The group drew its income from so many strands of the economy that airstrikes alone were not enough to cripple it.
Ledgers, receipt books, and monthly budgets describe how the militants monetized every inch of territory they conquered, taxing every bushel of wheat, every liter of sheep’s milk, and every watermelon sold at markets they controlled. From agriculture alone, they reaped hundreds of millions of dollars.
“We dismiss the Islamic State as savage. It is savage. We dismiss it as barbaric. It is barbaric. But at the same time these people realized the need to maintain institutions,’’ said Fawaz A. Gerges, author of “ISIS: A History.’’
“The Islamic State’s capacity to govern is really as dangerous as their combatants,’’ he said.
