Monday’s capture of Tel Abyad by the predominantly Kurdish YPG/YPJ forces in northern Syria represents a major defeat for ISIS just weeks after the jihadists’ string of victories in Iraq and Syria, in which they captured the towns of Ramadi and Palmyra. The defeat has surprised many, not least because Tel Abyad has long been considered a stronghold for ISIS.

Not only does Tel Abyad lie directly north of Raqqa on the Turkish border, but it also lies directly between the two Kurdish cantons of Kobani and Cezire. Taking Tel Abyad marks a breakthrough for the YPG/YPJ forces in that it gives the Syrian Kurds a 250-mile border with Turkey as well as uniting two of their three cantons.

Ever since the liberation of Kobani, the Syrian Kurds have had long-term aspirations to unite the three Kurdish cantons that make up Rojava, the de facto autonomous region of western Kurdistan. Linking Cezire — the biggest and most secure of the cantons — to Kobani has been considered essential in securing the latter, recently liberated canton after it was almost overrun by ISIS earlier this year. Until now, Tel Abyad has stood firmly in the way of such aspirations.

Much of the strategic importance of Tel Abyad rests on the fact that it borders the Turkish city of Akçakale, offering the easiest and most porous border for jihadists to cross into Syria from Turkey. Because of this, many believed it would take weeks to defeat ISIS from the city, but instead ISIS has capitulated under the pressure of US-led airstrikes and Kurdish advances. Suddenly, with their defeat in Tel Abyad, ISIS is left in control of just one single border crossing with Turkey, the town of Jarablus west of Kobani.

Kurds united, ISIS divided

With Tel Abyad secured, the Syrian Kurds have managed to forge a corridor between Cezire and Kobani. On Monday, images circulated on social media showing fighters from Cezire canton embracing those from Kobani. Such images underline the growing strength the Kurds have in northern Syria, and symbolize what is surely their greatest victory since the liberation of Kobani.

Throughout the siege of Kobani, the isolation of the city was the Kurds’ greatest vulnerability. With ISIS surrounding Kobani on all sides bar the Turkish border, Syrian Kurds in the other cantons — unable to reach the besieged city — watched helplessly as ISIS advanced. Even after the Kurds successfully repelled ISIS, the vulnerability of Kobani was all too clear.

Given that Tel Abyad was a launching pad for ISIS’ offensive into Kobani, many believed that Kobani would never be truly secure unless Tel Abyad was captured and liberated. As a result, the Kurdish party in Syria — the Democratic Peoples’ Party (PYD) — continuously asserted the need to take Tel Abyad in order to create a corridor between Kobani and Cezire, thereby strengthening their control of northern Syria.

The lack of mobility of fighters able to cross into Kobani was another major obstacle faced by the defenders of Kobani. While there was a continuous stream of fighters from different areas of Rojava and across Turkish Kurdistan, the more hardened guerrillas from the PKK could not come to their aid because smuggling in Turkey was considered too risky. But with the victory in Tel Abyad, the Kurds now for the first time control a stretch of land stretching from the Iranian border to Kobani, thereby allowing them to move freely between Iraqi Kurdistan and Kobani. This development will be a major boast for Kurdish military operations in Syria.

Where the victory at Tel Abyad marks a major breakthrough for the Kurds, whose ascendency has cemented them as the most powerful military force in northeastern Syria, the city’s capture represents a major setback for ISIS. Raqqa, the first major city that ISIS took and which is now considered the de facto capital of the so-called Islamic State, suddenly looks far more vulnerable. Tel Abyad will most likely be used as a base to launch further operations into Raqqa province, and the relative isolation of ISIS now will make the defense of their de facto capital much harder.

With no supply routes to Turkey between Kobani and the Iraqi border, ISIS’s only route to Turkey lies in the area west of Kobani. This new scenario seriously weakens ISIS’ ability to defend Raqqa, and initial reports of jihadists digging trenches north of Raqqa city indicate that they will not relinquish their control as easily as they have done in Tel Abyad.

Many accounts have emerged of limited resistance put up by the Islamic State as the Kurds entered the border town. ISIS jihadists were seen fleeing for Raqqa city, while others crossed into Turkey as local refugees fled from the fighting. This retreat marks a departure from ISIS’ earlier policy in Kobani, where the jihadists fought an unsuccessful four-month siege. It appears that ISIS do not want a repeat of this highly significant defeat, which certainly had a toll on their morale.

YPG/YPJ in Tel Abyad

While the capture of Tel Abyad is a major success, the question remains how easily the Kurds can retain control. Since most Kurds fled the area in the wake of ISIS’ advance into the city over a year ago, the vast majority of remaining civilians are Arabs. It is not clear how readily this local population will support the YPG/YPJ. Despite the presence of Arab battalions within their forces, many Arabs consider the YPG/YPJ to represent a purely Kurdish force. Likewise, many inside the YPG/YPJ remain distrustful of local Arabs, whom they suspect of being ISIS supporters.

With this in mind, the Kurds advanced into Tel Abyad under the banner of a coalition known as Burkan al-Firat (Euphrates Volcano), which includes battalions of the Free Syrian Army as well as the YPG/YPJ. Such unity between Arab and Kurdish units will be key in retaining the trust of the local Arab population, and it is a strategy with which the Kurds plan to continue to use in their offensive into Arab-majority areas.

Another important implication of this victory relates to Turkey’s role in the conflict. It is clear that the YPG/YPJ will put an immediate end to the continuous stream of jihadists crossing from the Turkish border city of Akçakale into Tel Abyad. Turkish President Erdoğan has already asserted his displeasure at these latest developments, but it is high time that Turkey rethinks its Syrian policy.

Turkey originally closed its border to refugees fleeing the conflict, and a video shows Turkish authorities watching on as ISIS jihadists drove the refugees away from the border. Furthermore, eyewitness accounts claim that hundreds of ISIS militants fled into Turkey disguised as refugees, further underscoring Turkey’s implicit support for the jihadists.

With the ruling AKP losing its majority in the recent elections in Turkey, much scrutiny has been directed towards Erdoğan on his policy towards Syria. Opposed to Kurdish plans for autonomy in northern Syria, the military successes of the Kurdish units will be a disappointing development for the President.

Turkey’s policy of opposing any Kurdish advances in Syria, alongside its tacit support for ISIS’s operations in the Turkish-Syrian border area, are becoming deeply problematic. Turkey now shares a 250-mile border with the Kurdish area of Rojava, and it is high time that they accept the PYD and the regional administration as a legitimate force and a crucial partner in the fight against extremism in Syria.