"If ISIS conquers the border crossing, Aleppo is isolated", explains Chapo Salah, the leader of the Kurdish Front. "There would be no way out." In the Kurdish stronghold north of Afrin, the PKK supporting Kurdish rebels fear an IS advance. A single raid by the well-equipped, well-organised soldiers of the radical Islamic State could see the last line of defence before Europe fall under the influence of the newly-formed Caliphate. "ISIS has almost laid hands on the North", Salah continues, "But not Azaz and the crossing to Turkey". Having long played a pivotal role in the resistance against the Assad regime in Damascus, Syrian Kurds from all over the region are joining forces with the Syrian Revolutionary Front and other rebel formations in a co-operative movement determined to stem the flow of IS ideology. "They are themselves not human - they cut our heads off", says Yusuf al-Halabi, a resident of Bab al-Salama. As more militia groups come together, threatened by a strain of Islam that considers their beliefs aberrant and heretical, Chapo Salah senses change: "This is new", he says. "At the beginning, we were alone".