How Big Is the Threat to Europe From Jihadis Fleeing Mosul?

There is a presumption that the fall of Mosul will result in a surge in attacks and terrorism back in the West. Europe in particular feels like it is in the group's crosshairs, with the refugee flow potentially masking a threat that will only magnify as the group loses territory on the battlefield in Iraq and more fighters want to leave the Islamic State militant group (ISIS). But this presumption is based on a potentially flawed set of assumptions about what will happen next and an understanding of how the terrorist threat has been evolving. Europe may face some terrorist incidents linked to a failing ISIS or other groups, but this threat is likely to simply continue much as before. It is unclear why ISIS would have waited until now to launch a surge of attacks.

Historically speaking it is hard to know where to look for a comparison with what we see happening in Iraq, and therefore what a precedent might look like. The most obvious comparison is the conflict in Afghanistan against the Soviet Union. In wake of Moscow's defeat, there was a chaotic situation in Afghanistan from which a flow of trained and ideologically motivated revolutionary warriors headed around the world. This produced extremist networks that expressed themselves in attacks for years to come under the banner of Al-Qaeda as well as insurgencies and civil wars in North Africa.

Yet this comparison is not completely accurate for the case of ISIS post-Mosul. The group may be losing one its major cities, but it still has a battlefield in Syria into which it can flow. Its territory there may be in retraction, but even if it loses it, the ungoverned spaces in the country mean it will be impossible to completely eradicate. And to look at a micro-level the individual fighters may make a varied set of choices: some may try to head home; some may seek other battlefields to continue the revolution; and yet others may simply change sides and continue to fight against the Assad regime under a different banner.

But more convincing still is the question of why the group would wait until now to mount some sort of attack. The Paris and Brussels attacks showed the group's capability and intention, and a number of subsequently disrupted plots show the group has been persistently trying, but so far seems to have failed to deliver any more blows. Instead, it has resorted to stirring plots from afar in the form of young people directed through encrypted communications to launch shocking low-tech plots. Some, like the murder of Jacques Harmel in Rouen, worked, while others, like the attempted attack outside Notre Dame cathedral in Paris, failed. And while a lot of these appear to be in France (and in that particular set of cases, directed by the same Rachid Kassim), there have been incidents in Australia, Germany, Indonesia and the U.K. that have similarities.

All of this suggests that the group is having difficulty pulling off another large-scale spectacular like Paris or Brussels, and is having to resort to instigating things from a distance. These can be equally atrocious and it is not, of course, impossible something large might still get through, but it is a question as to why the group would have waited until now to launch such an attack.

During Ramadan, the highly significant moment in the Islamic calendar that historically has been a depressing magnet for terrorist atrocities, the horrors the group was able to muster were a brutal bombing in Baghdad, alongside an attack on Istanbul's international airport. Horrors, yes, but in countries where they had substantial presence and ability to launch attacks—clearly something that they were unable at that moment to pull off in Europe.

Why the group is encountering this difficulty is likely a product of a number of things. In the first instance, it is clear that one of the attractions of the group was its success and strength on the battlefield. As this has waned, the number of those attracted has gone down. Second, coordination among security and intelligence agencies has likely gotten better; while there are still clear problems within some countries and coordination between their various security forces, they have also learned over time. Which of these is preeminent is unclear, but both will have an impact on the flow of fighters.

This is not to downplay the potential threat. One of the under-explored problems is the question of what to do with blocked travelers. As security authorities have faced the threat of terrorism from the battlefield in Syria and Iraq, they have learned and developed a deeper understanding of the nature of the threat and the networks getting people there. This has led to a growing number of people being prevented from traveling. The dilemma, however, is what to do with them then. In many cases, these are individuals who are motivated enough to want to go and fight, but find themselves abruptly unable to. This pent-up frustration can express itself in violence as people feel they want to do something, but are incapable of doing it. A number of attacks around the world have been linked to this phenomenon, including incidents in Canada, Australia, and France. This aspect of the threat may become larger as time goes on and the group becomes more inaccessible, while trying to stir people on further, but again, this is a trend that has been underway for some time already and it is not entirely clear why people would be more keen to do something for a group that was in recession.

Of greater concern instead is the potential ramifications to terrorist networks in third countries, like parts of southeast Asia, central Asia, the Middle East or north Africa. While forces in some of these countries are also improving, this has not been uniform and some notable gaps remain. In these places, the relatively easier trip may mean more decide to head home (rather than seek other battlefields or change sides in Syria) and this could produce instability and attacks.

ISIS's potential loss of Mosul is going to prove a significant moment for the group. But the threat from it is unlikely to change abruptly. Rather, the threat is likely to mutate and evolve, continuing to be a part of the fabric of the terrorist threat the world faces for some time to come.

Raffaello Pantucci is director of International Security Studies at the Royal United Services Institute (RUSI) and author of We Love Death as You Love Life: Britain's Suburban Terrorists.