Thousands of people from the United States, Europe, and other Western countries have run off to join ISIS. Exact numbers are difficult to discern, but of the more than 20,000 foreigners who have traveled to Syria and Iraq to join the so-called Islamic State, somewhere around 3,500 of them come from the West.

Their motivations vary from disenfranchisement with their own culture to being pissed off at their parents (no, really), and it is no secret that most of them are finding their way to Syria by crossing the border from Turkey. Meeting with several individuals in Kurdistan with inside knowledge of how this phenomena is taking place, SOFREP has identified a key choke point in the underground ratline that takes Westerners who want to join ISIS from their home countries to the Islamic State: Ataturk International Airport in Istanbul.

Named after the founder of the modern Turkish state, Kemal Ataturk, the airport is the largest in Turkey. After getting cyber-recruited by one of the many ISIS members conducting such activities on social media, the would-be jihadis hop on the airplane to Istanbul with instructions with what to do next.

The international terminal at Ataturk Airport is pretty much what you would expect from any major airport in America or Europe. Dozens of shops line the terminal selling fashionable handbags, duty-free liquor, and Starbucks coffee. One unique feature of the terminal is that it contains a mosque where Muslims who are traveling can go and pray while they wait for their connecting flights or prior to leaving the airport. I snapped a picture on a recent visit.

Prospective ISIS members are instructed to meet what we would call a link man, part of the ISIS underground network, in the mosque at the international terminal. The link man provides the young men with further instructions and enough money to get them to the border of Turkey and Syria. The Turkish government has faced some stiff accusations of colluding with ISIS, allowing the jihadis to traverse their borders while fighting the Kurdish YPG and YPJ fighters, as well as letting arms and jihadis from as far away as Chechnya and Georgia cross into Syria.

In conversations with Kurdish fighters, it seems they are well aware of this and have made the capture of Jarabulus one of their key objectives. Located between Kobani and Afrin, Jarabulus is the only place left in northern Syria where ISIS is on the Turkish border. If the Kurds are able to close the gap, a huge portion of ISIS’s logistics lines will suddenly dry up. Kurdish strategic thinking reckons that if they take down Jarabulus, Raqqa will fall into their hands with little fanfare.

For the Westerners traveling the underground railroad from Instanbul International Airport to Raqqa, a grim fate awaits most of them. The Iraqi and Syrian Baath party members are the real puppet masters behind the organization, and they have little interest in a bunch of confused angry kids from America or Britain in their ranks. From Raqqa they are spirited away to the front lines to be used as suicide bombers, packed into up-armored Humvees or MRAPs captured from the Iraqi Army and used as VBIEDs.

Many ISIS assaults open up with such suicide attacks, the opening salvo designed to take out Kurdish machine gun positions before ISIS assaulters moved forward. The YPG, YPJ, Peshmerga, and Zerevanni have lost a lot of men and women to these attacks, but thankfully, coalition airstrikes and the German government’s introduction of the MILAN Anti-Tank Missile System to the Peshmerga has made a big difference. Now the Kurds have a shot at fighting back.

However, to strike a death blow against ISIS, the coalition needs to not just defend against these attacks but rather go straight to the source. “If I know this, you think the Turkish government doesn’t?” a Kurdish official said in outrage over the Istanbul Airport fiasco. The Kurds have fought and killed these Europeans on the battlefield and are not at all happy about Turkey’s collusion with ISIS. Given that Turkey is a NATO member and a country that would one day like to join the European Union, perhaps it is time to address this issue with the Erdogan-led government.