In late January, the Kurdish forces of the People’s Protection Units, or YPG, declared that they had recaptured the northern Syrian city of Kobane, known in Arabic as Ein al-Arab.

The Kobane enclave has long been under siege by the jihadis of the so-called Islamic State, who were operating out of the surrounding Sunni Arab countryside. For months, the conflict rarely rose above low-level skirmishing. But in mid-September, after its victories in Iraq and eastern Syria, the Islamic State suddenly struck in force and threw the Kurds back to the border. As tens of thousands of Kurdish civilians fled in panic across the border to Turkey, the enclave seemed doomed to fall under complete Islamic State control—but then things turned around.

Raising the flag

The YPG and its all-female branch, YPJ, dug down in central Kobane, forcing the Islamic State attackers to engage in slow and costly house-to-house fighting. The time thus won proved crucial. Within a few weeks of the initial attack, the U.S. Air Force, which had intervened in Syria on September 22, turned its bombsights on Kobane.

Having initially viewed Kobane as a sideshow to the real war in Arab-majority Syria, the United States soon rearranged its priorities. Mounting media pressure played a part in this decision, but U.S. war planners must also have sensed an opportunity. Even though the United States views the YPG as representative of a particularly problematic strand of Kurdish nationalism, it couldn’t fail to notice that from a purely military point of view, the YPG also happens to be Syria’s most efficient jihadi-killing machine.

Thus, the tables turned on the Islamic State. By openly aligning itself with the Kurdish defenders and providing them with intense aerial support—from September until the end of 2014, three-fourths of all American air strikes in Syria took place in Kobane—the United States raised the symbolic stakes and turned Kobane into a death trap. Iraqi Kurdish peshmerga forces also arrived to aid the YPG. The Islamic State poured fighters into the city in a desperate attempt to finish off the last pockets of Kurdish defenders and rid itself of a far too costly battle. But over the following months, the combination of the YPG’s tooth-and-claw resistance on the ground and U.S. precision strikes from above proved too much to match.

Now, the Kurdish forces have recaptured Kobane City in its entirety. By January 26, YPG forces raised a 75-meter-long flag in the Kurdish colors of red, green, and yellow on Mistenur Hill, a height that overlooks the city. Since then, they claim to have retaken a further 120 villages in the Kurdish-majority areas around Kobane. Although there’s still some way to go before the YPG has restored the status quo ante, the battle that Carnegie’s Katherine Wilkens recently described on Syria in Crisis as a “Kurdish Alamo” seems to have ended in a resounding victory for the U.S.-Kurdish forces—an alliance that was as unexpected as it has proven effective.

A Pyrrhic victory?

That’s not to say that there will be a happy ending to the Kobane tragedy. Indeed, some have suggested that another historical metaphor might be far more fitting: wasn’t this in fact a Pyrrhic victory?

It is true that Kobane has been turned into a city of ruins. And enemies of the Islamic State should not get carried away by what happened there, because the success in Kobane will not be easy to repeat elsewhere.

Even though the YPG has proven itself a strong fighting force and a useful on-the-ground partner for the U.S. Air Force, it is at heart an ethnic self-defense militia—not an all-purpose tool for Western intervention in the Syrian war. The YPG’s effectiveness as an offensive force beyond Kobane will be sharply limited by Turkey’s hostility and refusal to provide aid across the border.

The ethnic barrier

In addition, the secular-leftist YPG’s poor relations with most of the surrounding Arab countryside and the Sunni-Islamist mainstream of the Arab opposition make it singularly ill-suited to lead an advance deeper into Syria.

Even as Kurdish refugees are beginning to trickle back into Kobane, there are reports of Arab civilians fleeing the YPG’s advance further south. Many are just trying to get out of the way of the war, but some surely fear that the victorious Kurds will now avenge themselves on Arab villages and families suspected of harboring pro-jihadi sympathies. That’s exactly what is now happening in northern Iraq, where the Islamic State had recruited local Sunni forces in a campaign of genocidal violence against the Yazidi religious minority. Having beaten back the jihadis, some Yazidis are now returning to loot and burn Sunni villages.

The Islamic State is of course exploiting Arab-Kurdish tension around Kobane as well, in the hope of rallying Arab locals to its side. The jihadis are said to have ordered military-age Arab males in the area to stay and help them defend their villages against the YPG, while allowing women and children to flee south to Raqqa. The deeper the YPG pushes into Arab territory, the uglier the ethnic warfare is likely to get.

Well aware of these limitations, the YPG leaders will certainly want to reclaim the rest of the Kurdish territory lost in September. If they succeed, they will perhaps also try to carve out a bit of a buffer zone to further fortify the enclave. But then, they’re in all likelihood just going to dig down and seek to rebuild Kobane.

Of course, the Kurds may still want to pursue retreating jihadi fighters, disrupt their transports and communications, and stage occasional raids on bases further afield in order to maintain pressure on the Islamic State—but they’re not likely to push their luck by venturing deep into Arab territory, unless offered something tangible in return.

Undermining the jihadis

For the Islamic State, this might be bad enough. One source of the jihadi group’s power was always its aura of invincibility. Rolling through the war-torn Sunni Arab peripheries of Syria and Iraq, the group has grown by absorbing disgruntled locals, former enemies, and minor armed factions, all of them eager to climb on the bandwagon instead of getting crushed under it. But now, having failed to defeat the U.S.-Kurdish coalition in Kobane, the Islamic State must seem a far less attractive option than it might have appeared to prospective recruits in northern Syria just a few months ago. Equally embarrassing setbacks in Iraq’s Mount Sinjar and elsewhere just add to the impression that the Islamic State’s 2014 winning streak has begun to fizzle out.

In addition, the YPG’s advances into the area around Kobane will put particular strain on the jihadis’ war effort in northern Syria. The strategic significance of the Kobane area is threefold:

The southern end of the enclave controls the east–west M4 road, which connects Aleppo to Hassakeh and Qamishli near the Iraqi border. The Islamic State remains in control of the main highway between Aleppo and Raqqa, but the YPG will weaken supply lines between Raqqa, al-Bab, and Manbij, the Islamic State’s strongholds east of Aleppo. By expanding along the border, the YPG could put pressure on the jihadi-controlled border towns of Jarabulus, across the Euphrates to the west of Kobane, and Tal Abyad, to the east. Tellingly, there’s already speculation about a raid on Tal Abyad. If the YPG retains U.S. backing and keeps up the pressure southward, this forces the Islamic State to fight on a longer front line and could enable raids, reconnaissance missions, and laser-designated airstrikes much deeper into its territory than was previously possible.

The Islamic State is a strong and flexible force and it has proved adept at controlling territory using limited means, ruling millions of people in Syria and Iraq. Reports that some of its forces are pulling back from positions east of Aleppo after the defeat in Kobane are thinly sourced so far, and it remains to be seen whether such troop movements are really a sign of weakness. But there is no doubt the group is overstretched.

It is true that Kobane is a small town and the battle to reclaim it was certainly costly. But this was no Pyrrhic victory. It was a serious military change of fortunes, a major event in Kurdish politics, and an ominous sign of things to come for the Islamic State.