ISIS fighters participate in a military parade in the northeastern Syrian city of Raqqa, on June 30, 2014.

ISIS fighters participate in a military parade in the northeastern Syrian city of Raqqa, on June 30, 2014. Raqqa Media Office/AP

Why Are Foreign Fighters Joining ISIS?

Foreign fighters participate in some of ISIS' 'worst acts,' but there isn't one clear explanation on why they join the battle in the first place.

In August 2014, ISIS marked Eid al-Fitr, the end of Ramadan, with a 20-minute, high-definition video offering its greetings to the Muslim world.

Gauzy images of smiling worshippers embracing at a mosque cut to children passing out sweets to break the Ramadan fast. These scenes were interspersed with shots of the muhajireen (Arabic for “emigrants”)—British, Finnish, Indonesian, Moroccan, Belgian, American, and South African—each repeating a variation on the same message.

“I’m calling on all the Muslims living in the West, America, Europe, and everywhere else, to come, to make hijra with your families to the land of Khilafah,” said a Finnish fighter of Somali descent. “Here, you go for fighting and afterwards you come back to your families. And if you get killed, then ... you’ll enter heaven, God willing, and Allah will take care of those you’ve left behind. So here, the caliphate will take care of you.”

Hijra is an Arabic word meaning “emigration,” evoking the Prophet Muhammad’s historic escape from Mecca, where assassins were plotting to kill him, to Medina. Abdullah Azzam, the father of the modern jihadist movement, defined hijra as departing from a land of fear to a land of safety, a definition he later amplified to include the act of leaving one’s land and family to take up jihad in the name of establishing an Islamic state. For most Islamic extremists today, the concepts of hijra and jihad are intimately linked.

A few months after the release of the Eid video, another ISIS production focused on the ISIS’s substantial foreign-fighter contingent in an entirely different way.

In a procession were a long line of at least 17 foreign fighters, many of them white-skinned Europeans, each guiding with his left hand a prisoner identified as a Syrian soldier. Only one wore a mask, the British fighter known as “Jihadi John,” who had executed James Foley and other American and European hostages.

After the jihadists had hacked through the necks of their victims, the camera played over the faces of the executioners, ensuring that they were clearly visible and sparking a rush to identify them. Media reports identified the perpetrators as French, German, British, Danish, and Australian citizens, although some of these claims were tentative.

ISIS propaganda and messaging is disproportionately slanted toward foreign fighters, both in its content and its target audience. Important ISIS messages are commonly released simultaneously in English, French, and German, then later translated into other languages, such as Russian, Indonesian, and Urdu.

“Foreign fighters are overrepresented, it seems, among the perpetrators of the Islamic State’s worst acts,” said Thomas Hegghammer, a leading scholar of jihadist history, in an interview with “So they help kind of radicalize the conflict—make it more brutal. They probably also make the conflict more intractable, because the people who come as foreign fighters are, on average, more ideological than the typical Syrian rebel.”

* * *

One of the most important questions about the threat presented by ISIS, and the conflict in Syria and Iraq in general, is numerical: How many foreign fighters are there, where do they come from, and what will they do after fighting?

The question is nearly impossible to answer with any kind of specificity, due to the dangers that ISIS presents for journalists and intelligence operatives on the ground. In the open-source world, there are only estimates, and the situation does not appear to be much better in the world of secret intelligence. According to one 2013 tally, from Radio Free Europe/Radio Liberty, there were between 17,000 and 19,000 fighters in Iraq and Syria, though this count is likely too low.

 The people who come as foreign fighters are, on average, more ideological than the typical Syrian rebel.
Thomas Hegghammer, scholar on jihadist history

The majority of those fighters originated in the Middle East and North Africa, especially Tunisia and Saudi Arabia. The remainder came from other places around the world, including former Soviet republics, the Americas, and Australia. But numbers were unavailable for several countries known to have provided fighters, including Azerbaijan, Indonesia, the Philippines, and Somalia. In general, moreover, foreign-fighter estimates are often unclear as to whether fighters are affiliated with ISIS and whether they pertain only to Syria or to Iraq and Syria.

Government estimates on the number of Americans who have joined ISIS have been wildly inconsistent. Based on both social-network analysis and anecdotal observation of comments by foreign fighters on social media, we believe that as of this writing, a minimum of 30 to 40 Americans are currently affiliated with jihadists in Syria and Iraq, in both fighting and noncombat capacities, and we estimate that well over a dozen are currently affiliated with ISIS. This figure represents what we can confidently assess from open sources, meaning the real figure is certainly higher, possibly by a wide margin.

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For the United Kingdom, similar disclaimers apply, but the range of estimates is much higher, especially on a per capita basis. In August, the United Kingdom estimated to reporters that 500 British citizens were affiliated with ISIS in Syria and Iraq, but dramatically higher estimates began to circulate toward the end of 2014. French- and German-speaking fighters have also been observed in large numbers on social media, and low-end estimates point to more than 550 fighters from Germany, and more than 1,000 from France. Significant numbers of Canadian fighters have also made their presence known on social media.

A typical jihadi foreign fighter is a male between 18 and 29 years old, according to a study by the Soufan Group, although there are many exceptions. Some are well over 30, and it is not uncommon to see fighters between 15 and 17.

Beyond age and gender, there are few consistent patterns and no reliable profile of who is likely to become a foreign fighter, but among Western recruits, a disproportionate number of converts can typically be found. (Converts are often especially vulnerable to fundamentalist ideas, often combining wild enthusiasm with a lack of knowledge about their new religion, making them susceptible to recruiters.) This approximate profile has endured for decades, through multiple jihadist conflicts.

* * *

Why do individuals travel abroad to take part in somebody else’s violent conflict?

There is no single pathway, no common socioeconomic background, not even a common religious upbringing among individuals attracted to foreign fighting in general or jihadist fighting in particular.

“Four decades of psychological research on who becomes a terrorist and why hasn’t yet produced any profile,” according to John Horgan, director of the Center for Terrorism and Security Studies at the University of Massachusetts Lowell, who has studied the subject intensively. While efforts to generalize about the problem have failed, he says, it is possible to understand some pathways for individuals.

Much of the research on why people join violent extremist groups boils down to a distinction between external and internal motives. External motives have to do with an individual’s perception of large-scale events in the world. While many analysts and policymakers have pointed to factors such as weak states, education, and social and economic disadvantage as external motivating factors, among those who study extremism in depth there is little consensus and much dispute on the importance of these factors.

There is no single pathway, no common socioeconomic background, not even a common religious upbringing among individuals attracted to foreign fighting in general or jihadist fighting in particular.

More often than not, the external factors cited by extremists themselves point toward the importance of much more specific situations, for instance, a military conflict or genocidal campaign, usually but not always involving victims from a potential recruit’s identity group.

Jihadist propaganda has often relied on exactly these flashpoints, such as the Soviet invasion of Afghanistan or the genocide in Bosnia, using them as points of entry to leverage narratives about the event, characterizing participation in the fight as not only a reasonable choice, but an obvious moral obligation. Indeed, jihadist ideologues often focus on the obligation of individual jihad when some or all of the ummah, or the Muslim nation, is under threat.

But these flashpoints do not necessarily provide adequate motivation on their own merits. They offer outlets, either for social pressures in a fighter’s native land or for his own internal struggles.

Internal motives stem from what an individual wants or needs for himself, in terms of the perceived benefits of membership in an extremist group, such as a feeling of belonging, escape into a new identity, adventure, or money. Foreign fighters have personal needs that are met by joining an organization, and those personal needs may become more important over time.

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According to Scott Atran, Western volunteers are often “immigrants, students, between jobs or girlfriends ... looking for new families of friends and fellow travelers. For the most part they have no traditional religious education and are ‘born again’ into a radical religious vocation through the appeal of militant jihad.” Social acceptance and reinforcement are important factors. Atran’s research found that three out of four foreign fighters in Syria traveled together with others, a figure consistent with previous studies on the subject. Traditionally, jihadist fighters have found internal motivation in the promise of perceived religious rewards such as entry into heaven. But for many, perhaps most, jihadists, religious motivations are necessary but not sufficient to explain the leap to violent action.

During the course of the civil war in Syria, the balance of internal and external factors has shifted over time. At the start of the conflict, a diverse coalition of imported religious fighters and secular Syrian rebels united loosely around the goal of overthrowing the oppressive Assad regime. For the jihadists, a longer-term goal was the establishment of a state governed by Islamic law, but the initial focus for most combatants was on fighting the regime. In the wake of ISIS’s rise, according to research by Peter Neumann, Scott Atran, and others, that goal has shifted noticeably to establishing Shariah law and supporting the institution of the caliphate, regardless of the wishes of the local Syrian population.

With the emergence of large numbers of foreign fighters on social media, it became possible to glean more about their internal motivations, which frequently went beyond the promise of heaven and turned instead to the theme of adventure. One British fighter, 23-year-old Ifthekar Jaman, coined the phrase “five-star jihad” to describe the fun he was having fighting in Syria, which caught on as a rallying cry to his countrymen, who showed up in ever-increasing numbers. (Jaman was killed in December 2013.)

A number of “celebrity” fighters upped the ante. One of the most popular was a former Dutch soldier named Yilmaz, who helped train fighters with various factions in Syria. He documented his Syrian experience on Instagram, posting pictures of battles and fighters, as well as images of the people of Syria, including children, and seemingly incongruous snapshots of jihadists cuddling with cats.

* * *

With the declaration of its “caliphate” in July 2014, ISIS began to enhance and amplify themes relating to the society it wanted to create, providing a new answer to the question: “Why join?” In his first speech as putative caliph, Abu Bakr al-Baghdadi reflected this new focus, calling on Muslims everywhere to make hijra “to the land of Islam” as a religious obligation. He went on: “We make a special call to the scholars, [Islamic legal experts] and callers, especially the judges, as well as people with military, administrative, and service expertise, and medical doctors and engineers of all different specializations and fields.”

In July 2014, ISIS’s Al Hayat Media Center released an 11-minute video, The Chosen Few of Different Lands, which drove this point home. A masterpiece of extremist propaganda, it showed a Canadian fighter named Andre Poulin, a white convert known to his comrades as Abu Muslim. The video opened with stunning high-definition stock footage of Canada (or a reasonable facsimile) as Poulin described his life back home.

“I was like your everyday regular Canadian before Islam,” he said. “I had money, I had family. I had good friends.”

The barbaric nature of ISIS can lead observers to conclude its adherents are simplistic, violent, and stupid. The Chosen Few displayed a keen self-awareness of this perception and actively argued against it, with Poulin as its telegenic exemplar.

“It wasn’t like I was some social outcast,” Poulin said. “It wasn’t like I was some anarchist, or somebody who just wants to destroy the world and kill everybody. No, I was a very good person, and you know,mujahideen [holy warriors] are regular people too. ... We have lives outside of our job.”

Life had been good in Canada, Poulin said, but he realized he could not live in an infidel state, paying taxes that were used “to wage war on Islam.”

In reality, Poulin was not quite the model of social integration that he portrayed on film. He developed an interest in explosives early and had dabbled in communism and anarchism before settling on radical Islam as an outlet for his interests. He had been arrested at least twice for threatening violence against the husband of a man whose wife he was sleeping with. These facts were conveniently omitted from his hagiography.

“He answered the call of his Lord and surrendered his soul without hesitation, leaving the world behind him,” said a narrator in perfect, unaccented English. “Not out of despair and hopelessness, but rather with certainty of Allah’s promise.”

At the end, Poulin spoke again, his visage filtered in a gauzy light.

“Put Allah before everything,” he said.

* * *

Many of ISIS’s most vocal and visible supporters online are women. Analysis of social networks linked to ISIS on Twitter found hundreds of users identifying themselves as women and actively spreading the organization’s message.

The leader of this online recruiting effort was a veteran of online agitation using variations on the online username “al Khansa’a”—the name of a female poet who was among the earliest converts to Islam in the days of the prophet, known for ordering her sons into battle on behalf of Islam. All four died. “I feel proud to be the mother of martyrs,” she is famously reputed to have said.

Al Khansa’a had been active on al-Qaeda-linked forums well before ISIS’s rise. Among members of the forum community, she was an early adopter of social media, opening a Twitter account under the handle @al_khansaa2 in September 2012, as well as establishing a presence on Facebook and other channels.

Aqsa Mahmood was another of the many women tirelessly working to recruit foreigners to join ISIS. As a teenager growing up in Glasgow, Scotland, she turned away from a typical, seemingly happy life spent consuming young adult novels and rock music and toward an increasingly militant outlook on the world and on her Muslim heritage, a sharp break from her family’s views.

Mahmood documented her transformation on Tumblr with all the enthusiasm a teenager can bring to bear, describing a swift transition from a mainly secular lifestyle into radicalism. “My parents genuinely think I’m extremist,” she wrote.

Her online friends—steeped in Salafist interpretations of Islam and the horror of the emerging Syrian civil war—became “the new family.” Throughout 2013, her writings turned more and more to openly jihadist ruminations and the growing obligation she felt to be involved in the struggle in Syria. In November, at the age of 19, she abruptly bid her horrified family farewell.

“I will see you on the day of judgment. I will take you to heaven, I will hold your hand,” her father recounted her saying. “I want to become a martyr.”

From Syria, she kept up her online activities, using Twitter and Tumblr to encourage others to follow her example. “And to those who are able and can still make your way, please [fear Allah] and don’t delay anymore, hasten hasten hasten to our lands and live in [honor],” she tweeted.

Uncounted other young women like Mahmood were lured to join ISIS in Syria and Iraq, including hundreds of Westerners and many more from Arabic-speaking countries.

“Most foreign girls will be married off to foreign fighters upon their arrival,” wrote Mia Bloom, a leading expert in the role of women in jihadist movements. “In fact, many are offered up as a form of compensation to the men fighting for al-Baghdadi.”

But the bricks-and-mortar al Khansa’a Brigade was a grim counterpoint to the illusion that its namesake sold online, according to one Syrian woman who defected from ISIS. In an interview with CNN, she described joining the brigade in Raqqa, Syria, where many ISIS foreign fighters were concentrated.

The defector, referred to as Khadija to protect her identity, told a jarring story of a women’s squad of morality police, who whipped women seen on the streets wearing anything that did not measure up to ISIS’s rigid ideal of female modesty.

* * *

ISIS has eschewed the al-Qaeda model of attracting fighters first and radicalizing them later. With its heady media mix of graphic violence and utopian idylls, ISIS sought recruits and supporters who were further down the path toward ideological radicalization or more inclined by personal disposition toward violence.

Once these pre-radicalized fighters and their families arrived in Iraq and Syria, they were exposed to an environment seething with traumatic stress, sexual violence, slavery, genocide, and death and dismemberment as public spectacles.

Among returning foreign fighters of previous generations—those that participated in the wars in Bosnia and Afghanistan, for example—perhaps one in nine would eventually take up terrorism on returning to their homelands. The fighters of ISIS are a new and untested breed. If they and their families someday attempt to return to their home countries, they will be unimaginably different from their predecessors.

ISIS has eschewed the al-Qaeda model of attracting fighters first and radicalizing them later. 

ISIS didn’t invent ultraviolent jihad. There have been many examples in the past, but they have led to consequences. In the horrific 1997 Luxor massacre in Egypt, 62 tourists (including women and children) were literally cut to pieces by dissident members of the Egyptian Islamic Group. The backlash led the group to moderate its overall approach.

The Abu Sayyaf Group has long beheaded hostages, sometimes on video, but its brutality and indiscriminate targeting have increasingly led to the perception that it is a criminal enterprise with expedient jihadist trappings.

But ISIS has crafted a novel formula for mixing brutal violence with the illusion of stability and dignity, and it has moved the bar for recruits. Its combination of successful ground strategy, aggressive messaging, and an appeal to strength over weakness has proven uniquely powerful and energized at least tens of thousands of ardent supporters.

The challenge that lies ahead for the group is whether it can sustain all three elements over time and whether its extraordinary capacity for violence will eventually alienate even its core supporters.

And if it survives the first two challenges, it will be faced with a third—whether its deliberate cultivation of ultraviolence as a core element of its society will lead it ever further into darkness, into a pit of horror that cannot be escaped.

This post has been adapted from Jessica Stern and J.M. Berger's forthcoming book, ISIS: The State of Terror.