Wearing the military uniform of Iraq’s élite counterterrorism force, Prime Minister Haider al-Abadi abruptly appeared on Iraqi national television in the early hours of Monday morning. “The time of victory has come, and operations to liberate Mosul have started,” he announced. The long-anticipated battle against the Islamic State—also known as ISIS, ISIL, or Daesh—for control of the strategic city was under way at last.

ISIS reconfigured Iraq’s borders in 2014, when it seized about a third of the country and declared its own Islamic caliphate. Now the battle is on to win back the territory. “Today, I declare the start of these victorious operations to free you from the violence and terrorism of Daesh,” Abadi said.

The announcement came just hours after ISIS lost Dabiq, a northern village of just over three thousand people in neighboring Syria. For two years, the Islamic State boasted that Dabiq was where Armageddon would play out in an apocalyptic battle with infidel forces from the West. The claim was based on Islamic prophecies from the seventh century. Despite its size, Dabiq has huge symbolic significance: it was a centerpiece of ISIS propaganda. In November, 2014, the British militant Mohammed Emwazi (Jihadi John) beheaded the American aid worker Peter Kassig there. In a video of the beheading, a narrator announced, “Here we are burying the first American crusader in Dabiq, eagerly waiting for the remainder of your armies to arrive.”

The loss of Dabiq, in Syria, and the launching of the largest offensive ever conducted against ISIS, in Iraq, led Obama Administration officials to predict that ISIS is finally being broken. “This is more than just the latest military result against this barbaric group,” Defense Secretary Ash Carter said in a statement. “The group carried out unspeakable atrocities in Dabiq, named its English-language magazine after the town and claimed it would be the site of a final victory for the so-called caliphate. Instead its liberation gives the campaign to deliver ISIL a lasting defeat new momentum in Syria.”

ISIS forces fled Dabiq when Syrian rebels, backed by Turkey and reportedly advised by U.S. Special Forces, pushed into the village, a senior Obama Administration official told me. “ISIL barely put up a fight,” he said. “They ran away, confronted with overwhelming force.”

ISIS is now losing both momentum and credibility. “This is a very bad week for ISIS,” Hassan Hassan, the co-author of “ISIS: Inside the Army of Terror_,”_ told me. “The loss of Dabiq is a huge blow. In the region, everyone from ordinary Muslims to Islamists to jihadists mocked ISIS for the loss of this town. The defeat at the hands of Syrian rebels is certainly embarrassing for the group and has undermined its external appeal, though the loss won’t affect the group’s internal coherence.”

The start of the battle for Mosul compounds ISIS’s woes. “ISIS is facing the test of a lifetime, and the only way to salvage its claims is if the battle fails, whether through military protraction or civilian abuse,” Hassan said. In the past, U.N. and U.S. officials and Iraq’s Sunni leaders have expressed concern about civilian casualties—and sectarian agendas—if Shiite militias advance on Mosul, where the majority of the population is Sunni.

U.S. officials said that two events in the past two months began turning the tide against ISIS. The first was the final assault, in August, on Manbij, a city of more than seventy-five thousand in northern Syria. It had served as a central hub of the ISIS supply routes by which goods were imported from the outside world and terrorists were exported to Europe.

“ISIL tried to hold Manbij, fighting until the last man, until the last days, but it lost badly,” the Administration official told me. “The operation broke the back of ISIL in the ‘Manbij pocket,’ where Dabiq is located.” The United States conducted more than fifty airstrikes on Manbij. More than twenty-five hundred ISIS fighters—including some of its most hardened foreign veterans from Chechnya and eastern Europe—were killed.

The second turning point, U.S. officials told me, was Turkey’s military intervention. Initially, it wasn’t fully coördinated with the U.S.-led coalition, but the U.S. Special Forces began working with the Turks to act in concert with Syrian opposition groups that were trained and supported by the Americans. Dabiq was the joint target. “ISIL resisted, and then just collapsed,” the Administration official said.

Over the past two months, ISIS has lost a number of top leaders in U.S. airstrikes: among them were its chief of external operations, Abu Mohammad al-Adnani, in August, and Wa’il Adil Hasan Salman al-Fayad, the minister of information and a member of the ruling Shura Council, in September.

The combined impact “demonstrates a rapidly crumbling ‘caliphate,’ ” the Administration official told me. “ISIL is under more pressure than ever before, and this pressure will only begin to accelerate further over the coming weeks.”

ISIS is now in danger of “a complete brand reversal,” Daveed Gartenstein-Ross, a senior fellow at the Foundation for Defense of Democracies, in Washington, D.C., told me. “Two years ago, they were thought of as strong, unstoppable, able to excite and mobilize followers, especially younger jihadists. Though the group still possesses real strengths, including its enormous success in carrying out terrorist attacks abroad, ISIS is in danger now of being seen as not only having overplayed its hand in Syria-Iraq but also having let its mouth write checks that its body can’t cash with respect to Islamic prophesy.” He continued, “We’ll see how ISIS’s opponents are able to capitalize, but this is a tremendous vulnerability for the group.”

Some thirty thousand troops—including tribal fighters, police officers, and Shiite militiamen—have been amassing for weeks on three frontiers to the north, south, and east of Mosul. The western front is the route to the rest of the Islamic State. This past weekend, Iraq signalled that the offensive was about to begin by dropping tens of thousands of leaflets over the city, a sprawling commercial hub. The leaflets advised residents to tape up windows, disconnect gas canisters, and coöperate with Iraqi troops when they arrive. “Keep calm and tell your children that it is only a game or thunder before the rain,” the leaflets said. “Women should not scream or shout, to preserve the children’s spirit.” ISIS is widely reported to have booby-trapped buildings, strategic installations, and roads in Mosul. It has also reportedly built tunnels under the city.

The United States has played a key role in coördinating rival Iraqi forces for the offensive—Sunni and Shiite Arabs in the Iraqi Army and some four thousand Kurdish troops in their own Peshmerga force. With the recent addition of another six hundred troops, the United States now has more than five thousand personnel deployed in Iraq and another few hundred Special Forces in Syria. In Iraq, the U.S. role is officially defined as “advise and assist,” but the advisers have basically designed the offensive, and have served as brokers between the Iraqis and the Kurds.

“We are proud to stand with you in this historic operation,” Brett McGurk, the U.S. envoy to the Coalition to Counter ISIL, tweeted as the offensive began. Lieutenant General Stephen Townsend, the U.S officer commanding the coalition, predicted that the operation—the largest since U.S. troops withdrew from Iraq, in 2011—“will likely continue for weeks, possibly months.”