Islamist fighters carry weapons as they demonstrate their skills during their graduation ceremony at a camp in eastern al-Ghouta, near Damascus November 28, 2013.
Islamist fighters carry weapons as they demonstrate their skills during their graduation ceremony at a camp in eastern al-Ghouta, near Damascus November 28, 2013.
Diaa Al-Din / Reuters

A decade ago, counterterrorism analysts around the world fretted about the possibility of European jihadists returning from the wars in Iraq and Afghanistan and finding safe harbor among embittered diaspora communities across Europe. But the al Qaeda “bleed out,” as it was called in counterterrorism circles, never really happened. The group didn’t take hold of North African and Middle Eastern communities in Europe. It failed to attract many of what the group called “clean skins”—Western passport holders able to slip through security without drawing attention.

The Islamic State (ISIS) has achieved in short order what al Qaeda could only dream about. Motivated by a call for jihad in Syria and connected via social media, second- and third-generation Muslim Europeans joined in droves to fight in Iraq and Syria. Their bonds grew tight; their propensity and their thirst for violence was insatiable. After helping build their caliphate in Syria and Iraq, these young European fighters have turned their guns on their homelands, with devastating effect. Brussels, Istanbul, and Paris—the violence has been steady and sustained.

Recent articles in The Wall Street Journal and Foreign Affairs suggest that ISIS is simply following the al Qaeda approach to terrorism in Europe. But such claims are off base. Al Qaeda sought to bring Westerners—clean skins—to terrorist safe havens, where the group would train them to follow detailed plans to attack designated high-profile targets. Trained cells and lone infiltrators were deployed back to their homelands in pursuit of al Qaeda’s bidding. These disciples had little autonomy and were directed to strike at high-profile targets. ISIS’ European jihad looks very different from that of its al Qaeda forefathers, and it is far more dangerous for Europe.

An Iraqi Shi'ite fighter walks past walls painted with the ISIS flag, November 24, 2014.
An Iraqi Shi'ite fighter walks past walls painted with the ISIS flag, November 24, 2014.

ISIS’ greatest advantage in Europe comes from its many years of cultivating foreign fighter networks to Syria. Much has been made of al Qaeda leader Osama bin Laden’s Arab legion fighting in Afghanistan during the 1980s, but that force’s numbers paled in comparison to today’s cadres of European ISIS members, which is likely tenfold larger. Fast communication over social media and easy travel into Turkey has facilitated the unprecedented flow. Al Qaeda’s recruitment efforts faced more challenges. The group never enjoyed the level of technological sophistication that is available to ISIS. It relied more on physical facilitation and brought in far fewer newcomers, who were incrementally assessed and slowly integrated into Pakistan, Afghanistan, Yemen, and the Sahel—all locations that were far more difficult than Syria to traverse. Although ISIS has chewed up its international cadres in staggering numbers during routs like the one in Kobani, the European survivors of ISIS will still far outnumber the foreign fighters al Qaeda managed to recruit.

The recruits ISIS has brought in are, in some ways, more valuable than those al Qaeda used to win over. Al Qaeda desperately sought clean skins for the execution of Western plots. But the Westerners they attracted proved to be few and far between. They were often troubled souls, and some ultimately caused discord in the ranks, eventually becoming more of a liability than a benefit. Omar Hammami and Osama al Britani, a famous American foreign fighter and a famous British foreign fighter for al Qaeda’s affiliate al Shabab in Somalia, challenged their emir, Ahmed Godane, and created a rift between foreign and local fighters. Their public dissension increased discord in al Shabab’s ranks and ultimately led to the public killing of these previously celebrated Western recruits.

Lacking adequate access to recruits with Western passports, al Qaeda instead settled for Arab men able to travel into the West on visas. External operations cells sought intelligent, disciplined recruits; many of al Qaeda’s operatives thus had college degrees, came from well-respected families, and appeared highly capable. Although many of them went through training in Afghanistan, few dispatched to the West had significant combat experience. Their attacks were their initiation into violence. They were rookies operating in enemy territory, and as primarily Middle Eastern and North African men, they routinely drew attention. Sometimes they managed to get through—9/11, of course, is the prime example—but often they were stymied as they crossed borders, coordinated plots against airlines, or tried to develop explosive devices to attack transportation systems.

ISIS has turned al Qaeda’s recruitment pattern on its head—to spectacular effect. Its recruits come in packs from European diaspora neighborhoods. Unlike al Qaeda, which heavily screened incoming members to weed out potential spies or those with criminal pasts, ISIS, at least at its height in 2015, took in any foreigners that volunteered, giving the disenfranchised a new home, purpose, and direction. Nearly half of those identified in connection to the Paris and Brussels attacks had criminal records prior to joining, including for such offenses as carjacking and bank robbery. Al Qaeda was correct that a criminal history would be a disadvantage when sending one or two infiltrators to the West at a time. But the wave of returning ISIS fighters has overwhelmed European screening systems. Some returnees have, of course, been picked up. But the many have traveled back home without being interdicted and using nothing more than their passports.

ISIS attacks in the West appear empowered rather than hindered by the less pious and more brazen criminal recruits the group has attracted. First, ISIS’ European veterans have settled back into the very neighborhoods and communities (sometimes sympathetic to their cause) that they came from, drawing minimal security scrutiny, a luxury al Qaeda never had at such a scale. Second, ISIS operatives attack towns and targets that they know intimately. Instead of having to conduct extravagant reconnaissance on unfamiliar national monuments or government targets, they’ve gone after local sports venues, transportation hubs, and popular public places that they might well have frequented.

Third, ISIS operatives in the West are often related to each other or are lifelong friends, having been recruited together, served side by side, and returned intact as a fighting unit. Their extended relationships have built trust and commitment during attacks on the West that al Qaeda only garnered among its oldest cadres from Afghanistan. And fourth, ISIS foreign recruits’ past criminality demonstrates a predisposition for nefarious activity and violent conduct prior to heading out for jihad in Syria and Iraq. They are likely more comfortable with killing than al Qaeda recruits, and as a result, are more confident and committed to their attacks when they return.

A fighter from al-Qaeda aligned rebel group Jabhat al-Nusra runs with his weapon as their base is shelled in Raqqa province, eastern Syria, March 14, 2013.
A fighter from al Qaeda-aligned rebel group Jabhat al-Nusra runs with his weapon as their base is shelled in Raqqa province, eastern Syria, March 14, 2013.
Hamid Khatib / Reuters

ISIS’ recent success in Europe stems from its access to numerous well-trained European fighters. But its operational approach has helped the group along. Al Qaeda plodded slowly, micromanaging its external operations with persistent contact between their operatives and central headquarters. The group’s plots were complex to a fault, and were highly controlled by senior leaders back in Afghanistan and Pakistan. This slowed the pace of attacks globally.

Because ISIS fighting units are experienced and tight-knit, they can pursue a model more similar to the U.S. military’s concept of Commander’s Intent. As retired U.S. Army Reserve Special Forces officer Chad Storlie explained in Harvard Business Review, “Commander’s Intent describes how the commander envisions the battlefield at the conclusion of the mission. It shows what success looks like. Commander’s Intent fully recognizes the chaos, lack of a complete information picture, changes in enemy situation, and other relevant factors that may make a plan either completely or partially obsolete when it is executed. The role of Commander’s Intent is to empower subordinates and guide their initiative and improvisation as they adapt the plan to the changed battlefield environment.”

ISIS’ external operations cell leaders have the autonomy to plot and plan locally, pursuing Mumbai-style attacks more reminiscent of the Pakistan-based Lashkar-e-Taiba’s 2009 raids in India. Such attacks can be planned quicker and better than any scheme hatched by less informed ISIS senior leaders bogged down in the day-to-day management of the caliphate. The wild successes of Paris and Brussels breed further success as copycat attackers mobilize across the West. Most fail or achieve little, but sometimes, as in the case of San Bernardino, they succeed and further boost the aura of ISIS whether they were connected to the group or not.

ISIS’ Commander’s Intent approach, as opposed to al Qaeda’s micromanagement, also produces fewer signals that could allow Western governments to detect impending attacks. Al Qaeda plots were often tipped off by increases in “terrorist chatter”—increased signal patterns suggesting a cell may be in pre-attack mode. The sustained back-and-forth that allowed al Qaeda central to maintain operational control was a liability. But Commander’s Intent allows subordinates to communicate less frequently with headquarters. And ISIS has rapidly adopted increasing levels of encryption via a host of social media applications and other cyber techniques that were simply not available during al Qaeda’s heyday.

ISIS’ vast manpower and diffuse operational control poses serious threats for Europe in the near term. The autonomy and flexibility of the terrorists will outpace the slow plodding of a patchwork of EU bureaucracies. Over the long term, however, ISIS’ European approach may turn on itself. Their brash violence has killed many innocent civilians, including Muslims, women, and children. Al Qaeda’s current leader, Ayman al-Zawahiri, pursues a cautious, slow approach for attacking the West to avoid losing popular support that might arise from such casualties. He learned this lesson during his days leading the Egyptian Islamic Jihad, when their widespread killing of civilians helped bring their expulsion from the country.

Should ISIS’ aggression reach new levels in the West, it may start to sour what little public support it has. This doesn’t mean that the West can be complacent, though. Ultimately, it will have to look to see what other terrorist groups, whether international or domestic, try to replicate—and build on—in ISIS’ success. Europe’s vulnerabilities have been exposed. If ISIS doesn’t exploit them, some other terrorist group or criminal enterprise will.

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