Islamic State has lost its capital in Syria: What happens now?

After four months of grueling street fighting, a U.S.-backed Syrian force said Tuesday that it had wrested control of Raqqah from Islamic State, dealing a powerful symbolic blow to the militants who made the city the de facto capital of their self-styled caliphate.

Celebratory gunfire erupted in the shattered metropolis along the Euphrates River, where years of airstrikes left virtually no building unscathed. Video and photographs shared on social media showed members of the Syrian Democratic Forces, or SDF, raising their yellow flag and spinning doughnuts in armored vehicles at an infamous traffic circle where the militants would force residents to watch gruesome beheadings and crucifixions.

More than any other city, Raqqah came to embody the towering ambitions and brutal excesses of Islamic State. For three years, it was home to many of the group’s leaders, a place where foreign captives were imprisoned and killed, where Yazidi women and girls were sold into slavery and where attacks were launched around the world.

But most of the senior leaders left months ago, heading south toward the border with Iraq and their remaining strongholds in Dair Alzour province. Many commanders and fighters gathered in the town of Mayadeen, which was recaptured Saturday by the Syrian government and its Russian and Iranian allies.

Those who remained in Raqqah mounted a final stand at the main hospital and sports stadium, where fighting raged over the last two days.

“We are in control of the whole city,� Mustafa Bali, a spokesman for the Kurdish-led SDF forces, said Tuesday. “The stadium was the last place to be liberated, and our forces are cleansing the area and removing bombs to open main roads inside the city.�

A formal victory declaration would come later, he said, after troops had cleared the city of explosive devices and any militants still in hiding.

The U.S.-led coalition battling Islamic State said about 100 extremists were still holed up in a sliver of the city that is heavily booby-trapped and mined. One of these devices killed a senior SDF commander Monday, according to Col. Ryan Dillon, a U.S. military spokesman in Baghdad.

“We understand that there is still about 10% of the city that has to be cleared, and we still expect there to be pockets of resistance in those areas,� he said.

Raqqah’s fall is the latest in a string of military defeats for Islamic State, which the coalition says has lost 87% of the territory it controlled after a lightning sweep across vast stretches of Syria and Iraq in 2014.

Iraqi forces captured the group’s most prized possession, the northern Iraqi city of Mosul, in July. The militants are now clustered in a handful of towns on either side of the Syrian-Iraqi border.

Though the establishment of a modern-day caliphate, or Islamic state, served as a powerful recruiting tool for the militants, U.S. commanders caution that its collapse does not spell the end of an ideology that has inspired deadly attacks around the world.

There are already signs that some of the militants are transforming themselves into a more conventional guerrilla-style insurgent force. The group, which is often referred to by the acronym ISIS, also has active branches in other parts of the Middle East, Africa and Asia.

In Syria and Iraq, Islamic State leaders have proven adept at exploiting long-standing grievances among Sunni Arabs, who often saw them as defenders against their countries’ corrupt and abusive leaders even if they did not always embrace the militants’ extreme interpretation of Islamic law.

Those grievances remain unresolved and could be tapped again, analysts say.

“In a sense, we’ve been at this moment before, when there was a U.S.-led surge in Iraq from 2007 that people who fought it thought had defeated Islamic State in Iraq, which is the precursor entity to ISIS,� said Peter Mandaville, a former advisor in the U.S. State Department who was part of a team implementing the U.S. strategy to counter the militants in 2015-2016.

“I understand that the Syrian Kurdish forces that were at the forefront of this very impressive victory are quite ebullient and excited right now,� said Mandaville, who is now at George Mason University’s Schar School of Policy and Government. “That said, I also think there is the risk of a little too much euphoria and triumphalism around this.�

Syrian Democratic Forces, backed by coalition air power, began their assault on Raqqah in early June. Much of the city now lies in ruins, its buildings pulverized by artillery fire and airstrikes that killed more than 1,000 people, according to local activists and foreign monitoring groups.

Hundreds of survivors who were being held as human shields were able to make their escape in recent days under a controversial deal negotiated by tribal leaders and a provincial council that also saw the surrender of 275 local extremists and their families.

They are among about 270,000 people displaced from Raqqah, crowded into camps where conditions are miserable and families do not have enough food, water or medicine.

“With high levels of destruction reported in and around Raqqah, most families have little or nothing to return home to and will likely be stuck in camps for months or years to come,� the international aid group Save the Children said in a statement Tuesday. “In addition, more than 10,000 people a day are now fleeing ongoing fighting in ISIS strongholds around Dair Alzour.�

Once Raqqah is fully liberated, its future remains uncertain. A civilian council made up of Kurds and Arabs is poised to take charge of running the city. But the Syrian government is determined to regain control of the areas it lost to the uprising against President Bashar Assad.

U.S. officials envisage that their role will be limited.

De-mining, removal of rubble, setting up electricity and supplies of clean water are the next tasks for the United States, State Department spokeswoman Heather Nauert told reporters in Washington on Tuesday.

"We will restore basic services, not [do] the nation-building that the U.S. government previously engaged in in other countries," she said. The idea, she explained, "is to get it up and running and then turn it over to other countries and the host country."

Nauert did not address a question about the fact that in this case the "host country" is in the midst of a civil war and many in Raqqah might fear retaliation from the Assad government.

Meanwhile, there is already concern among some U.S. lawmakers that the capture of Islamic State’s most well-known stronghold could lead to complacency about the continuing fight against the group.

"We should celebrate the fall of ISIS in Raqqah and the liberation of those who were living under terrorist oppression,� said Sen. Ben Sasse (R-Neb.), who sits on the Senate Armed Services Committee. But he cautioned that this is “no time to let off of the gas.�

The city’s capture “underscores the need for a comprehensive Syria strategy because our military, our partners and allies, and those brave souls who are literally fighting for their homes and for their neighbors deserve nothing less than our full commitment to see this through," Sasse said in a statement.