Thaier Al-Sudani / Reuters

Iraqi forces, backed by U.S. airstrikes, retook the central part of Fallujah from the Islamic State on Friday in an assault to end the three-year-long occupation of the city 40 miles from Baghdad.

Two U.S. airstrikes destroyed six heavy machine guns and 10 fighting positions. Iraqi forces, though, received minimal resistance from the Islamic State when they entered the central part of the city on Friday. This came as a surprise, as The New York Times reports:

The rapid, and unexpected, gains suggested a shift in tactics by the Sunni extremists of the Islamic State, also known as ISIS or ISIL, or perhaps a sign of their weakness, as they abandoned their dug-in positions and regrouped in western neighborhoods. That allowed thousands of civilians, which aid groups had said were being held as human shields, to flee across two bridges over the Euphrates River beginning on Thursday.

Even as the battle appeared far from over, Iraqi commanders on the ground were optimistic that the advance, which had slowed in the face of Islamic State snipers, roadside bombs and tunnel networks that allowed fighters to move around undetected, would continue.

Since the U.S. invasion of Iraq in 2003, Fallujah has been a hotspot for the extremist insurgency. Most notably, in 2004, the city was the site of one of the deadliest assaults on American troops in the entire war, leading to the birth of Al Qaeda in Iraq.

Fallujah had been under the Islamic State’s grasp for longer than any other city in the region. Fighters were supported by local tribal leaders, who the Times reports backed out of the fight there when it looked as if an Iraqi victory was inevitable. As many as 60,000 people left the city during the fight, having lived for months in poor conditions, lacking enough food, medicine, and clean drinking water.

We want to hear what you think about this article. Submit a letter to the editor or write to letters@theatlantic.com.