In February of 2015, the Islamic State of Iraq and Syria's victory march across the Middle East began to end. Its first major loss came in the Syrian town of Kobane, where it was beaten back by Kurdish fighters and American airstrikes. The next month, ISIS lost control of the Iraqi city of Tikrit, defeated there by Iraqi troops, Shia militias, and more American airstrikes.
The summer brought more difficulties for ISIS, which would lose some 25 percent of its territory in Iraq and Syria. The group, meanwhile, sought to establish new "caliphates" in failed states — in Libya, Afghanistan, and Yemen — and in each would find only modest, and temporary, success.
That October, two ISIS members, using the names Ahmad al-Mohammad and M al-Mahmod and traveling under fake Syrian passports, arrived at the Greek island of Leros. They made their way to France or to Belgium, where they met up with several other members of ISIS, most or all of whom were European nationals. In November, in Paris, they helped launch one of the deadliest terror attacks in modern European history, killing 130 people.
On Tuesday, terrorists struck the Belgian capital of Brussels, killing at least 26 people at a downtown train station and the city's airport. It bore the hallmarks of an ISIS attack, and before long the group's media arm claimed responsibility.
In the coming hours and days, there will be inevitable debate over how or whether Belgian or European security officials failed in preventing this attack. But the hard truth is that such attacks may, to some degree, simply be Europe's future.
European security officials had for weeks been "bracing" for an attack like what came to Brussels. As Belgian Prime Minister Charles Michel put it, "What we feared has happened." Everything we know about ISIS's leadership, its fighters, and Europe suggests that this danger will remain with them; these threats will continue and perhaps even grow. Europe will have to learn to manage this threat and live with this fear.
As ISIS loses its state, it is shifting emphasis to terror attacks
The world of violent jihadism is a competitive one, and ISIS's greatest rival has always been al-Qaeda. Their antagonism has many roots, some going back decades, to the war in Afghanistan, but it is today expressed both as literal war in Syria, where they fight for territory, and as a broader but more abstract war of ideology, over which group can rightfully claim the mantle of jihadism's global vanguard.
ISIS took the lead in that war early, by doing something al-Qaeda had never accomplished: declaring an actual state, stretching across Iraq and Syria. This, along with its string of stunning battlefield victories in 2014, allowed ISIS to build something of a jihadist super brand. With its narrative of success and invincibility, it recruited thousands of fighters, swelling its ranks, building further on its self-reinforcing momentum.
But when ISIS began to lose its caliphate — its territory chipped away by Kurdish groups, Shia militias, the Iraqi army, and US-led airstrikes — the narrative of victory and invincibility began to collapse as well. If it wanted to maintain its ideological strength, from which it partially derives its military strength, it would need to find a new way to prove itself, a new way to capture global headlines and attention.
It found the answer in coordinated terror attacks against civilians. Unlike al-Qaeda, which chose difficult and (in its view) strategic targets such as embassies or the Pentagon, ISIS chose the most vulnerable, because this would sow the most terror and do the most human damage. It tested this strategy in June 2015, in the Tunisian tourist town of Sousse, where it killed 39 people. It worked.
"If you're experiencing territorial losses, how do you make up for that? Well, pivoting to asymmetric warfare makes a lot of sense," terrorism expert Daveed Gartenstein-Ross told my colleague Zack Beauchamp recently. "You can impose a cost on countries for being part of an effort to beat you back."
This also allowed ISIS to hit back — or at least portray itself as hitting back — against its enemies in the West, inverting the narrative of Western airstrikes as humiliating the group.
"I think it has made the calculation that it can no longer pursue its expansion strategy in Syria and Iraq without changing the calculations of the enemies currently halting its expansion," Will McCants, also a terror expert, told my colleague. "These attacks would be a way of inflicting costs on them."
ISIS was probably always going to lose its "caliphate." The group simply does not have the resources or capability to run a mini state for long. It is surrounded by enemies who are far more powerful and bent on its destruction. For the past year, we've been watching the ISIS mini state crumbling right before our eyes.
As that happens, the group's leadership seems to have concluded that its best response, in simple strategic terms, is to coordinate large-scale terrorist attacks abroad: 100 people in Ankara, a Russian airliner over Egypt, 43 people in Beirut, the Paris attack.
"If an extremist group that has seized territory starts to lose it, it will be highly incentivized to turn to terrorist operations that allow for maximizing effects at a lower cost," Clint Watts, another terrorism expert, wrote in War on the Rocks shortly after Paris.
ISIS is all but certain to continue losing ground in Iraq and Syria, and its efforts to establish new "caliphates" seems doomed as well. It survives, ideologically and militarily, on momentum, and that momentum will inevitably shift into more large-scale attacks against civilians, including in Europe.
"ISIS is a state that has millions of dollars that it can spend on these kinds of operations," McCants went on. "We're not talking about al-Qaeda hiding out in Pakistan. We're talking about an actual government that has money to put behind plots and has very motivated people, many of them with European passports that can carry them out."
The group's resources — money, weapons, officers with experience planning military operations, veteran fighters with experience carrying them out — are substantial. Those resources will increasingly go toward more attacks like that in Brussels.
Europe's terrorist threat comes from Europeans, not foreigners
There is a myth, propagated by Western political leaders who wish to halt immigration or at least exploit popular fear for their own electoral gain, that Europe's terrorist threat comes from refugees.
In fact, it comes from fellow Europeans. And that makes the problem much more difficult for Europe to solve. You can close borders or shut down immigration (or at least try). But when the threat comes from your own citizens, it's a threat you can only manage and maybe never fully solve.
The Paris attackers, for example, were mostly or all European nationals. Salah Abdeslam, the last surviving ISIS member who has been accused of helping lead the attack, and who was arrested just a few days ago in Belgium, is in fact a Belgian-born French national.
The reasons a European national might join ISIS are disputed by experts. The only thing these experts can agree on is that "radicalization," as its called, is enormously complex, and the reasons vary from individual to individual. Some cite the social and political marginalization of Muslim communities in Europe; some point to the estrangement and isolation inherent in youth; others mention ISIS's propaganda skills in exploiting these trends.
The point is that this is a complex problem that stems from preexisting communities within European societies, not a problem of outsiders that can be solved with anything as simple as closing a border.
Consider this chart, from a December report by the Soufan Group, on the sources of foreign fighters in Syria and Iraq:
That report found that the number of Western recruits had more than doubled in the previous year alone — even as European governments had instituted new measures meant to limit the ability of Europeans to reach Syria and Iraq.
A number of Europeans are now fighting with ISIS, gaining connections and battlefield experience. As the group weakens in Iraq and Syria, more of those fighters will inevitably return home to Europe. The threat they pose will grow.
It gets worse: Within Europe, these militants are able to plug into existing organized crime networks, which can help with logistics and supplies as well as with smuggling people across borders.
"The mingling of two entirely separate worlds — organized crime and violent Islamic extremism — has hugely complicated the task of tracking down suspects," Vivienne Walt wrote recently for Time magazine.
"This makes the situation extremely difficult for intelligence, because it is two different networks with two different logics," Claude Moniquet, a former French intelligence official, told Walt.
Organized crime is a problem that has existed in Europe for centuries. It is a problem that can and should be managed, but it's nothing that can be decisively "solved" any more than European officials can outright solve the problem whereby socially isolated youths become susceptible to extremist propaganda online.
In other words: If you want to fix the terrorist threat, you've got to defeat ISIS, resolve complex socioeconomic problems going back generations, and end organized crime.
ISIS will become what it was before: a terrorist group capable of terrible damage
The trajectory here seems frighteningly clear: ISIS will lose most or, perhaps inevitably, all of its caliphate. But once that happens, it will revert to something like its previous form, when it was a terrorist group known as al-Qaeda in Iraq, or AQI.
AQI emerged during the chaos of the Iraq War, in the mid-2000s, during which time it developed many of the brutal techniques we now associate with ISIS: videotaped beheadings, terror attacks against "soft" civilian targets, an ideology of sectarian ultraviolence.
In that form, AQI never had military successes as dramatic as ISIS, and it never established a mini state. It was "just" an insurgency and terror group, hiding out in the ungoverned and anti-government corners of the failed state of Iraq. In that form it was able to do terrible damage, including by launching large-scale terror attacks.
The difference is that AQI's terror attacks focused on targets within the Middle East, most infamously in Jordan. That fit within AQI's strategic and ideological mission at the time.
But now ISIS has both the means and the impetus to direct such attacks more widely, both within the broader Middle East and against targets in the West. Once its caliphate collapses, it will lose some of those resources but will retain more than enough to continue these sorts of attacks.
In this form, ISIS will continue to pose a danger to the world, but it will become far harder to defeat. As a terrorist insurgency, it will not require the trappings of statehood but merely requires state failure in Iraq and Syria from which to operate.
Defeating ISIS in this form would require more than the world may be capable of accomplishing anytime in the near future.
In Iraq, it would require not just defeating ISIS but also occupying ISIS-held Sunni regions to wipe out the insurgency, then reintegrating those regions into the Iraqi state, convincing suspicious Iraqi Sunnis they are better off buying into a political system that has never earned, and has frequently abused, their trust. While Iraq did this once before, in the late 2000s, it took a years-long and extremely costly American-led military occupation, along with many Iraqi sacrifices, and even then it lasted only briefly.
It would require a peace deal to end Syria's war, so that ISIS's enemies will stop fighting one another, turn against ISIS, and, in a process that would likely take years, restore order and national unity. And those are just the things that would need to happen before Syria underwent its own Iraq-style process of occupying and reintegrating Sunni regions.
These are tasks that will take, in the best case, years to accomplish, and maybe more. And even then, some version of an ISIS insurgency may persist with enough resources and strength to continue coordinating large-scale attacks.
In the meantime, Europe's terrorism problem is something it will have to simply manage and, at times, endure. That will mean providing security, without overreacting in ways that only help terrorists by disseminating the fear they desire or by punishing the refugees who are both innocent and themselves victims of the same groups. It will mean addressing at-risk individuals or communities without overpolicing them or otherwise treating them as the enemy when they're not.
That is not a case for defeatism, and it's certainly not a case for fear, which only strengthens the terrorist groups. Terrorism is still a threat that kills far fewer Europeans than other kinds of crime — much less than, say, automobile accidents. But it is precisely to combat that fear, and the dangerous far-right politics it promotes, that Europeans will have to understand that this is part of their reality now.