This is part four of a four-part series.
By late February and early March, it had become a common scene on the far outskirts of the northeastern Syrian town of Baghuz: evacuees from the Islamic State terror group's final scrap of territory huddled on the desert floor, empty water bottles littering the ground as they waited to be vetted and taken to a displaced persons camp.
Only something had changed. These huddled masses were no longer civilians trapped by the terror group's steady retreat or those who had been held as slaves or prisoners.
These women and children were the families of the IS fighters, many of them from outside Syria and Iraq. And they were unabashed in making one thing clear.
"I don't want to go back," Dorothée Maquere, the wife of French foreign fighter Jean-Michel Clain, told television cameras for the French news agency AFP.
"Let France leave me alone," she added. "They killed my husband, my children, my family. That's it. It's finished."
Maquere had plenty of company. By the time Baghuz finally fell, U.S.-backed forces had captured more than 2,000 foreign fighters and nearly 8,000 of their wives, children and relatives, many of whom had chosen to stay.
More may still be at large. A U.N. report issued in February estimated that of the 14,000 to 18,000 IS fighters active in Iraq and Syria at the time, up to 3,000 were foreign fighters.
And those estimates may be low.
U.S. and Syrian Democratic Forces officials admit they vastly underestimated both the size of the IS force and the fighters' civilian family members hunkered down for a last stand in Baghuz.
Many may have also joined Iraqi and Syrian IS fighters who chose to shift away from the pressure as the SDF closed in on their shrinking territorial holdings.
"ISIS fighters in Syria responded to the loss of a territorial 'caliphate' by crossing the border into Iraq and taking refuge in that country's northern and western desert regions," U.S. Principal Deputy Inspector General Glenn Fine, using an acronym for the group, wrote in the latest report on Operation Inherent Resolve, the U.S.-led effort to destroy the caliphate.
So, too, there are indications foreign fighters have found a way to hide, at times, in plain sight.
According to coalition officials, IS maintains a series of "well-supplied" clandestine cells throughout Syria and Iraq, many just on the outskirts of major urban centers.
Unknown factors
And many current estimates often cannot account for IS numbers in parts of Syria where the U.S. and U.S.-backed forces are not able to operate.
"We have much less insight into what's going on in [Syrian] regime- and Russian-controlled areas," according to a senior U.S. defense official, speaking on the condition of anonymity given the sensitive subject matter. "We're concerned and we have regular conversations with the Russians about the idea of this ISIS fight moving out of areas that the coalition controls."
Officials with the U.S.-backed coalition also worry that across Syria and Iraq, IS still benefits from pockets of support among Sunni Arabs and some tribal leaders, which may give foreign fighters additional options.
"A lot fewer moved back to their countries of origin than had been suspected," Seth Jones, director of the Transnational Threats Project at the Center for Strategic and International Studies, told VOA. "I think they've done a reasonable job of blending in and waiting to fight for another day."
Still more foreign fighters may have left without going very far.
"There are also reports that foreign fighters are lying low in countries outside of Iraq and Syria, essentially biding their time until conditions are suitable for their return," said Jade Parker, a former counterterrorism analyst in support of U.S. military activities.
Not everyone is convinced, and there is disagreement about the extent to which IS foreign fighters have been able to entrench themselves in areas once controlled by the group's caliphate.
"When they lose territory, it is very difficult for them to integrate those folks [the foreign fighters] into what the rest of the locals are doing," Craig Whiteside, a senior associate with the Center on Irregular Warfare at the Naval War College, said regarding the terror group's clandestine activities.
"Their transition to insurgency does not include foreign fighters," he said.
Yet even if foreign fighters are not aiding in the insurgency now, it may just be a matter of time.
Continued entry
Even as the IS caliphate crumbled and countries like Turkey worked to shut down transit routes to Syria, coalition officials said handfuls of foreign fighters were still finding ways in.
And spirits among the remaining IS fighters are improving.
"The morale of ISIS fighters in Iraq increased since last quarter, because of the weather improving and the influx of fighters returning from Syria," the most recent U.S. inspector general report on counter-IS operations in the Middle East concluded.
"Core ISIS is the main game still in terms of the threat," said Linda Robinson, a senior researcher with the RAND Corporation, a global policy research group.
"We have about six to 12 months before a kind of full-blown insurgency could come back to life and a level of violence that goes beyond what the state [Iraq] is capable of managing," she said.
U.S. Central Command officials have given similar assessments for Syria, "absent U.S. counterterrorism pressure."
Even the IS foreign fighters and their families in SDF custody are a growing cause for concern.
The U.S. has been pushing for Western countries to take them back and prosecute them, though officials admit some countries are still struggling to develop the necessary legal framework. But these officials say dealing with those issues can be put off for only so long.
"It's an immediate problem," Alina Romanowski, the State Department's principal deputy coordinator for counterterrorism, said at a recent forum in Washington.
"You can't just let them wander around the globe for however long they're going to be around, but they're also in these detention camps," she said. "They're recruiting like crazy. And what are we doing about that?"
