The US has led the creation of a large coalition to defeat ISIS since 2014, but it never accounted for what to do if large numbers of ISIS members surrendered. When tens of thousands were detained in Syria, especially women and children of male ISIS fighters, Washington realized it had a problem.Today, that problem is even more acute as the US weighs how to leave Syria. Legally, it is problematic for the US to transfer ISIS fighters it doesn’t hold to the Syrian regime or other countries. The Syrian Democratic Forces (SDF), a mostly Kurdish force the US helped create in 2015, is required to hold the fighters, even though the US doesn’t recognize the SDF’s legal status. According to Pentagon Inspector-General reports on the US-led Operation Inherent Resolve, there are around 10,000 ISIS fighters detained in eastern Syria by the SDF. The US says that between 1,200 and 2,000 of them are foreign fighters. They are thought to come from as many as 50 countries. There were 800 European ISIS members held in June, and it is thought that most remain in Syria. There are also around 35,000 women – believed to be ISIS supporters – being held in the Al-Hol camp. Many of them are Iraqis and Syrians. They have set up their own internal ISIS police in the camp, and the SDF only controls the outside of the facility.Although President Donald Trump announced on October 6 that the US was going to leave part of Syria, he said on October 23 that the SDF would continue to keep the ISIS members under “strict lock and key.” The US had also claimed on October 6 that European countries refused to take their ISIS citizens back and that the US would not hold them, leaving Turkey responsible for ISIS fighters in the area captured over the past two years.Now, the US has decided that Turkey is not responsible. But the US faces a problem. Because Washington didn’t want responsibility for the ISIS fighters that its anti-ISIS coalition helped capture, the US foisted them onto the SDF and has told it to hold them. America helped create the SDF in 2015 from portions of the Kurdish People’s Protection Units. This was to create a non-sectarian organization that the US could work with. The SDF was not told at the time it would be contracted and expected to hold tens of thousands of ISIS members. The US trained up to 100,000 SDF members – around 70,000 of them to deal with internal security issues, including guarding detainees. In only rare examples have ISIS members gone home and been repatriated. After the US decided to withdraw, it ordered a raid to take at least two high profile members out of Syria. But the rest remain.The US State Department has excluded the SDF from the Geneva discussions about the future of Syria. The US envoy to Syria and the anti-ISIS coalition, James Jeffrey, says that Washington has no “permanent relationships with substate entities.” This is how the US views the SDF: as a substate contractor to deal with security and hold ISIS members, so that wealthy Western countries don’t have to deal with them. In this way, one of the poorest regions of Syria is expected by the UK, US, France, Germany and others to house their ISIS citizens and other ISIS members. The SDF is not allowed to let the ISIS members go; it can’t transfer them to Iraq, the Syrian regime, or Turkey.The US needs the SDF as a substate contractor to detain the ISIS members because if the US were to secure them, then it would be legally responsible for them. As it is, the ISIS members don’t legally exist. They are not prisoners of war, and they are not held by a government. The coalition that is fighting ISIS doesn’t hold any prisoners. This is the legal fiction created so that it appears no one has any responsibility. However, the Pentagon reports clearly lay out that the detainees are a looming problem. The SDF doesn’t have the resources to house what amounts to a small city’s worth of ISIS members and their families. Humanitarian organizations have now left parts of eastern Syria because the Syrian government has signed a deal with the SDF. But the Syrian government and Russia don’t want the ISIS members either. The UK won’t even take back the children of its citizens that joined ISIS. After all, if the UK took them back, then it would be admitting some responsibility. Quietly, UK special forces are exiting areas in eastern Syria as if they were never there. They can get on transport helicopters and planes. But no kids are allowed. No one has told those children that they don’t really exist officially and that the most powerful countries in the world went all the way to Syria to fight ISIS, but couldn’t be bothered to repatriate their own citizens.