The tiny Syrian village of Dabiq was to have been the site of an apocalyptic showdown between Christian and Muslim armies, an Islamic version of the battle of Armageddon that would herald the end of the world, according to ancient prophecies embraced and trumpeted by the Islamic State.

Instead of waging an epic battle, however, the last Islamic State fighters defending Dabiq fled Sunday without a fight in the face of an advance by a small force of Free Syrian Army rebels, backed by Turkey and by U.S. airstrikes.

The loss of Dabiq was of more symbolic than strategic importance to the wider war, a fresh humiliation for the Islamic State, which lured volunteer fighters from around the world with promises of building a mighty Islamist empire.

It also offered further evidence of the Islamic State’s rapidly diminishing capabilities ahead of the imminent offensive targeting the city of Mosul in neighboring Iraq.

The battle for Mosul, expected in the coming days, promises to be the most consequential yet of the two-year-old campaign against the Islamic State, which is also known as ISIS and ISIL. Mosul is the biggest of the cities controlled by the Islamic State, one of the two capitals of the group’s self-proclaimed caliphate, and its supporters are expected to put up a tough fight, said Col. John Dorrian, a spokesman for the U.S. military in Baghdad.

“Daesh has been in Mosul for two years, and they’ve had the chance to build some pretty elaborate defenses,” Dorrian said, using the Arabic acronym for the Islamic State. “We’ve prepared the Iraqis for a tough fight.”

Coming on the eve of the Mosul battle, the defeat at Dabiq serves as a further blow to the militants’ morale, a reminder that they are continuing to lose ground across their rapidly shrinking territory in Iraq and Syria, he said.

“Daesh said there was going to be an apocalyptic battle here. That has not proven to be the case, and now Dabiq is Daesh-free,” Dorrian said.

The ease with which the opposition force overran Dabiq surprised even the rebels, who have been steadily advancing through villages controlled by the militant group in the countryside of northern Aleppo province in the weeks since Turkish troops intervened to support them in the fight.

A few dozen U.S. Special Operations forces also are in northern Syria assisting the rebels. Dorrian declined to say whether they had played any direct role in the Dabiq conquest, citing operational security.

The plan had been to lay siege to the village, where the rebels had expected the militants to put up at least a token defense, given its symbolic value, according to Abu Jalal, a commander with the U.S.-supported al-Hamza Division, one of half a dozen groups affiliated with the Free Syrian Army that took part in the offensive.

But as the rebels moved Sunday to capture the last road leading south out of Dabiq, the remaining 100 or so Islamic State fighters there ran away, Abu Jalal said. They were pursued by U.S. warplanes, which struck them in at least two locations, he said.

Islamic State commanders repeatedly promised their fighters in Dabiq that reinforcements were on the way, Abu Jalal said, but none arrived.

“This shows that the illusion ISIS planted in its supporters’ minds was just an illusion. They retreated without a fight,” he said. “It proves that ISIS is one big lie and that they could be finished in all of the region soon.”

“Even ISIS members no longer believe their commanders because they realize everything they tell them is a lie. ISIS is now in a very weak position, and their morale is low.”

The village’s significance dates to a seventh-century saying, or hadith, of the prophet Muhammad, who had reputedly predicted that Dabiq would be the site of an epic showdown between Muslims and Christians, the equivalent of the biblical battle of Armageddon. The confrontation would herald the advance of Muslim armies toward Constantinople and eventually to Rome, before culminating in the end of the world.

The Islamic State had put this prophecy at the center of its propaganda, naming its monthly magazine Dabiq and choosing the village as the site of the execution of one of its most prominent American hostages, aid worker Peter Kassig.

Few Muslims outside extremist circles attach any particular significance to the village, one of dozens of nondescript settlements across the rolling farmland of northern Syria. “For us, Dabiq is just like any another village, any other battle in any area,” Abu Jalal said.

The Islamic State appeared recently to have foreseen its demise in the village. Without explanation or announcement, last month it quietly renamed its flagship magazine Rumiyah — an ancient term for Rome, now an even more distant prospect than ever.

Zakaria reported from Istanbul.