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Book Review Roundtable: Foreign Fighters in the Armies of Jihad

In this roundtable, our contributors review Daniel Byman's book "Road Warriors: Foreign Fighters in the Armies of Jihad," which provides a sweeping history of jihadist foreign fighters from Afghanistan in the 1980s to the civil war in Syria.

1. Introduction: The Foreign Fighter Dilemma

Stephen Tankel


Earlier this summer, counter-terrorism experts and diplomats at the United Nations finished negotiating the biennial review of the Global Counter-Terrorism Strategy, which had been postponed in 2020 due to the outbreak of COVID-19.1 The resolution does not have the force of law, but it does provide a normative framework for how the United Nations and many of its member states should combat terrorism. Among the most critical issues, the repatriation of foreign terrorist fighters who traveled to join the Islamic State in Iraq and the Levant (ISIL) was arguably the most pressing and the most controversial. While the United States has called on states to take back their nationals — foreign fighters and their families — European allies, like the United Kingdom, and various other countries have strongly opposed repatriation, staking out strong public stances that will make it hard to back down.2

Foreign fighters began traveling to Syria after civil war erupted there in 2011. Their numbers surged after ISIL seized control of swathes of Syria and Iraq in 2014 and declared a caliphate.

By the time of ISIL’s territorial defeat in March 2019, over 40,000 individuals from 110 countries had traveled to Iraq and Syria, with the majority of them joining the group.3 This was the largest convergence of jihadists in history, and one that set off alarm bells in capitals around the world. Although the waves of foreign terrorist fighters traveling to Iraq and Syria subsided as ISIL’s territorial caliphate collapsed, roughly 10,000 ISIL fighters and about 60,000 women and children are being held in a series of prisons run by the Syrian Democratic Forces. Most of the fighters are Syrian or Iraqi, but as of November 2020, the United Nations reported that at least 1,500 of those being held were foreign fighters from other countries.4

While states scrambled to find ways to halt the flow of foreign terrorist fighters, researchers attempted to understand why the Syrian civil war and then the rise of ISIL attracted so many of them. The study of foreign fighters was not new. There was plenty of material for me to sift through, for example, when writing a Masters’ dissertation on their role in the Bosnian conflict. Nevertheless, the sheer volume of individuals traveling to Iraq and Syria, their importance to ISIL, and the potential threats that these individuals posed to their home countries and the international community contributed to a larger effort among scholars and analysts to understand the foreign fighter phenomenon. No single volume could capture all the facets of this phenomenon, but Daniel Byman’s Road Warriors: Foreign Fighters in the Armies of Jihad offers a stellar and accessible account of foreign fighters over the past half-century.

In Road Warriors, Byman defines foreign fighters as “individuals who travel to a state other than their own to join an illicit group and perpetrate or assist in terrorist attacks or armed conflict.”5 He focuses on jihadist foreign fighters — those associated with al-Qaeda and ISIL and their affiliated groups — and eschews individuals who might have travelled to another country to fight with Shiite militias (e.g., Lebanese fighters who fought under the command of the Iranian Revolutionary Guards-Quds Force in Syria) or white identity extremists fighting in Ukraine.6 This focus makes sense given that most foreign fighters are motivated by jihadism rather than by other causes.

Byman tells the story of the jihadist foreign fighter movement by interweaving individual biographies and a historical narrative. Indeed, the book is not only a sweeping history of jihadist foreign fighters, but also an important addition to the historical canon of the modern global jihadist movement. Kim Cragin identifies Byman’s use of individual biographies as a major strength of the book, which she considers to be the most comprehensive one yet written on foreign fighters and their global impact. Cragin nevertheless laments that Byman’s approach sometimes overlooks what she terms “supporting characters” who were often instrumental in the history that he is recounting. She also takes issue with the fact that Road Warriors tends to focus on foreign fighters who have had an impact on the West at the expense of their significance elsewhere. For example, Cragin notes that Algerian foreign fighters played a critical role in their country’s civil war, but are only referenced in regard to their involvement in attacks in Europe during the 1990s. Even the most comprehensive books have gaps. As Cragin notes, the ones in Road Warriors do not detract from its overall contribution to our understanding of jihadist foreign fighters.

Thomas Hegghammer and Aaron Zelin view this contribution through the lens of Byman’s ability to tease out common threads running through the history of foreign fighting. Zelin credits Byman with identifying and unpacking key trends at the state, network, and individual level. The strength and durability of foreign fighter networks is one of those threads. In tracing individual foreign fighters, Road Warriors demonstrates that members of the main foreign fighter contingents that emerged over the last several decades had connections to one another. These individuals were “professional jihadi[s] not tied to one particular struggle,” and many of them fought on multiple jihadist fronts.7

Another recurring theme in the history of the foreign fighter movement is the role that states played. Zelin in particular takes note of Byman’s recounting of how many governments took a laissez-faire attitude when it came to their nationals leaving to fight on jihadist fronts. Road Warriors not only captures this dynamic, but also the subsequent actions that many of these same governments take to strip their nationals of citizenship or block their return. Hegghammer views this dynamic through a complementary lens, which informs his Cheese Bell Theory. This theory holds that functioning states are like cheese bells in the sense that they crush all minor forms of rebellion inside their jurisdiction. Hegghammer argues that foreign fighting has become a mechanism for escaping the counter-terrorism efforts of these states. This helps to explain why, as Byman’s book illustrates, jihadists have often been more successful as foreign fighters than as domestic revolutionaries.

If Hegghammer’s Cheese Bell Theory is correct, then reducing opportunities for foreign fighting will hamper the jihadist movement overall. The massive outflow triggered by the Syrian civil war and then the rise of ISIL led governments to take the issue much more seriously than they had in the past. Of course, even if future foreign fighter flows are limited, this still leaves the many thousands of individuals who have already left to fight abroad. Byman concludes that the most that counter-terrorism officials can do is minimize the potential damage that these foreign fighters can cause. Yet, as he also notes, U.S. efforts against foreign fighters since 9/11 have been quite successful. Cragin adds that other countries have also worked diligently to enact measures to manage the threat. What most governments have failed to do is to find a solution for the thousands of individuals still being held in Syria. This failure highlights the challenges that dealing with foreign fighters can pose and the urgent need to prevent or at least contain future flows. Byman’s book diagnoses many of the factors that have allowed the jihadist foreign fighter phenomenon to flourish and offers original and concrete policy suggestions to supplement the countermeasures already in place. This makes it an important scholarly contribution to the terrorism literature and a useful guide for policymakers and practitioners.


Stephen Tankel is an associate professor at American University, an adjunct senior fellow at the Center for a New American Security, and an associate editor at Texas National Security Review. He has served on the House Foreign Affairs Committee and in the Office of the Under Secretary of Defense for Policy. Tankel is the author most recently of With Us and Against Us: How America’s Partners Help and Hinder the War on Terror.


2. On the Road: A Closer Look at Jihad’s Foreign Fighters

R. Kim Cragin


In Road Warriors: Foreign Fighters in the Armies of Jihad, Daniel Byman traces the history and experiences of foreign fighters sympathetic to the Salafi jihadi movement. Byman defines foreign fighters as “individuals who travel to a state other than their own to join an illicit group and perpetrate or assist in terrorist attacks or armed conflict.”8 Road Warriors focuses exclusively on foreign fighters associated with al-Qaeda, the Islamic State, and their affiliated groups, eschewing individuals who might have travelled to another country to fight with Shiite militias (e.g., Lebanese fighters who recently fought under the command of the Iranian Revolutionary Guards-Quds Force in Syria) or mercenaries for hire.9 Within this context, Road Warriors concludes that the threat posed by jihadist foreign fighters is significant and is likely to increase in the future, given both the historical role of these fighters in international terrorist attacks and their tendency to regionalize local civil wars.10

The book deftly interweaves several different stories. It explains the emergence of Salafi jihadism as an ideology, the expansion of al-Qaeda and its successor, the Islamic State, as well as efforts by Western countries, in particular, to address these threats. The stories are held together through a series of more detailed discussions of infamous foreign fighters from within the Salafi jihadi movement: Palestinian Abdullah Azzam, Saudi Abd al Rahman al Dawsary, Jordanian Abu Musab al Zarqawi, American Omar Hammami, British Mohammad Emwazi, and several others.

Abdullah Azzam remains one of the most significant personalities in the early history of al-Qaeda and foreign fighters.11 Azzam articulated and popularized the religious justification for individuals to become foreign fighters in his 1984 treatise entitled Defense of Muslim Lands, which he wrote in an effort to generate support for the fight against Soviet forces in Afghanistan.12 Happily, Road Warriors gives Abdullah Azzam his due. The book also nods to other important voices from the Afghan jihad, namely Algerian Abdullah Anas and Egyptian Mustafa Hamid, who wrote firsthand narratives of the experiences of foreign fighters in Afghanistan during the 1980s and 1990s.13 Interestingly, both Anas and Hamid have since been highly critical of al-Qaeda, the Islamic State, and newer generations of foreign fighters.

In contrast to Azzam, Abd al Rahman al Dawsary (aka Abu Abdel Aziz Barbaros) cannot be considered as having an outsized role in the narrative arc of foreign fighters. Barbaros travelled with four companions from Pakistan to Bosnia in April 1992, soon after the conflict in Afghanistan had ebbed. He, along with approximately 3,000 foreigners, fought alongside Bosnian Muslims against the Serbs.14 It is hard to argue that Barbaros deserves the same weight of consideration as Azzam. Nevertheless, Road Warriors correctly observes that, after the 1995 Dayton Accords, many foreign fighters remained in Bosnia.15 They settled in Gornja Maoca, Osve, and Dubnica, villages that have served as recruitment hubs for Islamic State foreign fighters over 20 years after the Dayton Accords.16 Additionally, in the intervening years, authorities in France, Italy, Spain, and Turkey all dismantled terrorist cells with ties to foreign fighters who had participated in the Bosnian war.17

Road Warriors also gives significant attention to Abu Musab al Zarqawi, the former leader of al-Qaeda in Iraq and arguably one of the most well-known foreign fighters.18 Al Zarqawi left Afghanistan in December 2001 with approximately 50 supporters, making his way from Zahedan to Mashhad and eventually Tehran, where he was promptly arrested.19 Upon release, al Zarqawi and his supporters travelled to Iraq and began to build a logistics network to bring other foreign fighters into the country, in anticipation of an invasion by the United States.20 This logistics network — sometimes referred to as a facilitation network — emanated out of Syria and was run by a Syrian facilitator named Sulayman Khalid Darwish, another foreign fighter who had returned home from Afghanistan.21 Approximately 5,000 foreign fighters eventually came to Iraq to fight for al Zarqawi. The United States has estimated that they were responsible for nine of 10 suicide bombings between 2003 and 2008.22

The strength of Road Warriors is its interweaving of individual biographies, such as al Zarqawi’s, and a historical narrative. But this approach also has some inherent weaknesses. Namely, in focusing on a handful of key individuals, the book tends to overlook what some people might consider supporting characters. For example, Road Warriors correctly attributes both an increased emphasis on brutality and a turn toward sectarianism in the Salafi jihadi movement to al Zarqawi.23 Yet it does not discuss other foreign fighters, such as Syrian Sulayman Khalid Darwish, Egyptian Abu Yaqub al Masri, or Abu Usama al Tunisi, who were instrumental to Zarqawi’s campaign. Road Warriors similarly provides a detailed discussion of Mohammad Emwazi, one of the so-called Islamic State “Beatles,” who was responsible for beheading journalists James Foley and Steven Sotloff.24 But it does not discuss another British foreign fighter, Sally-Anne Jones, who, along with her husband Junaid Hussein, has been linked to over a dozen Islamic State attacks and plots in the West.25 Indeed, an estimated 7,000 women left their homes and travelled to Syria to join the Islamic State26 — more than the total number of male foreign fighters who had previously joined al Zarqawi in Iraq — and yet their stories are absent from Road Warriors.

Road Warriors also tends to focus on foreign fighters who have had an impact on the West and, as a result, underplays their significance elsewhere. For example, approximately 4,900 Algerians returned home from Afghanistan to fight — several in leadership roles — in Algeria’s civil war during the 1990s.27 They represented 40 per cent of the total fighting force for the Armed Islamic Group (GIA) in a civil war that resulted in over 100,000 casualties. Yet Road Warriors only addresses the GIA in a chapter on jihadists in Europe, namely the GIA’s 1995 attacks in France.28 Road Warriors, similarly, hardly touches on Indonesia, which sent approximately 850 foreign fighters to Afghanistan in the mid-1980s and, more recently, a similar number to Syria. One of Indonesia’s more famous Afghan vets, Iman Samudra, helped to orchestrate the October 2002 attacks in Bali, which killed over 200 people, including 88 Australian and 23 British citizens.29

Despite these absences, Byman’s Road Warriors is the most comprehensive book on foreign fighters and their global impact, tracing the metastasis of their ideas and tactics from generation to generation. It is perhaps unsurprising, in this sense, that Byman concludes on a pessimistic note, arguing that all counter-terrorism officials can really do at this point is minimize the potential damage of these fighters. (I have found that most academics and intelligence analysts who focus on foreign fighters have a somewhat grim outlook.) Yet, Byman also presents some good news. Namely, he stipulates that U.S. efforts against foreign fighters — military and law enforcement — post-9/11 have been remarkably successful. My research has led me to a similar conclusion.30 I would add that other countries, such as Australia and Spain, to name a few, also have worked diligently to enact measures to halt the metastasis. So maybe the future is not quite as grim as we fear.


R. Kim Cragin, Ph.D. is a senior research fellow at the National Defense University. She is a widely published expert on counter-terrorism, foreign fighters, and terrorist group adaptation. Cragin was formerly a senior political scientist at the RAND Corporation and also has taught as an adjunct professor at Georgetown University and the University of Maryland. The opinions expressed here represent her own views and are not those of the National Defense University, the Department of Defense, or the U.S. government.


3. Foreign Fighters and Cheese Bells

Thomas Hegghammer


Few topics in international security have captured as much attention in recent years as that of foreign fighters. A Google search for the term now yields over a million hits, while Google Scholar suggests it features in some 20,000 publications, three-quarters of which are from the 2010s. Interest among policymakers has been similarly high: Since around 2013, many countries around the world have implemented measures to combat foreign fighting, and in 2014 the phenomenon even got its own U.N. Security Council Resolution.31

The reason for the surge in attention was, of course, the departure of unprecedented numbers of Islamist volunteers to fight in Syria’s civil war between 2012 and 2016. In this period, tens of thousands of Muslims from all over the world, including over 5,000 from Europe, joined the Syrian rebellion. A large proportion of them ended up joining the Islamic State (ISIL), the world’s most formidable terrorist organization at the time, prompting fears that they would not only fuel the ranks of jihadism in the Middle East, but also pose a global terrorist threat.

For the same reason, the academic literature on foreign fighters is heavily centered on the case of Syria in the 2010s, which has been studied in depth from several angles.32 An important line of inquiry has been the individual-level characteristics and recruitment pathways of the fighters.33 Another has been the in-theatre activities of the fighters and their impact on their host organization and the Syrian conflict.34 Yet another has been the prospect of so-called blowback or spillover from travelers to Syria in the form of international terrorist attacks.35 To be sure, the literature has not been exclusively focused on ISIL volunteers. In fact, a byproduct of the increased general interest in foreign fighting has been studies into little-known variants of the phenomenon, such as far-right, Shiite, or anti-ISIL foreign fighting.36 Still, the Syrian jihadi case looms larger, to the point where, in the public consciousness, the term foreign fighter has become closely associated with ISIL volunteers.

Enter Daniel Byman’s new book Road Warriors, which takes a long historical view on the phenomenon of Islamist foreign fighters. The book shows with great clarity that foreign fighters who went to Syria in the 2010s are but the latest in a long series of jihadi foreign fighter mobilizations and that the phenomenon needs to be understood — and dealt with — as the decades-old and wide-ranging phenomenon that it is. Byman’s account starts in 1980s Afghanistan and passes through early-1990s Bosnia, mid-1990s Chechnya, late-1990s Afghanistan, mid-2000s Iraq, and late-2000s Somalia before reaching the Syrian civil war. He then looks at the repercussions of jihadi foreign fighting in Europe and the United States before ending with an in-depth reflection on what can be done to counter the phenomenon.

Road Warriors is an extremely valuable addition to the literature. It is the first long history of jihadi foreign fighting and, as such, it allows us to see patterns and nuances that are less apparent. It is also highly accessible, making it very well suited as an introduction to the topic for newcomers. Byman’s clear prose and his organization of the book into chronological chapters centered on key individuals constitute a breath of fresh air in a sometimes dense academic literature. At the same time, the book is packed with details and insights that even jihadism specialists will learn from.

Of particular value is the chapter on countermeasures, in which Byman presents an innovative framework for thinking about the constituent parts of the foreign fighter challenge and offers policy suggestions that are as specific as they are original. In books with such breadth of scope, there will always be minor quibbles to be had about details of specific cases (I had a few for 1980s Afghanistan) and about editorial decisions (I would have liked, for example, to see a nod to pre-1980s cases, such as the 1948 Palestine war or the late 1960s Islamist Fedayin). None of this, however, detracts from the fact that Road Warriors is a highly accurate synthesis of a complex literature and is a major academic achievement.

Three Features of Jihadi Foreign Fighting

The story told in Road Warriors brings out three important macro-features of jihadi foreign fighting that merit highlighting. The first is continuity. The book shows that all the main foreign fighter contingents are connected, not just in the sense that they represent the same type of activity, but in the sense that we find some of the same people in several different conflict zones. Abu Abdel Aziz Barbaros in Bosnia had also fought in Afghanistan, Ibn Khattab in Chechnya had fought both in Afghanistan and in Tajikistan, and Abu Musab al Zarqawi in Iraq had previously fought in Afghanistan in both the 1980s and 1990s. Some of the men who went and fought in the Syria civil war, such as Abu Firas al Suri, had resumés going back to the 1980s. In my recent book The Caravan, I mention the case of Abd al Aziz Ali, an Egyptian in the 1980s Afghan jihad who also fought in Palestine in 1948.37 This continuity is in addition to the considerable ideological continuity across contingents  — exemplified by the influence of Abdullah Azzam’s writings on post-1980s foreign fighters — as well as the shared sense of history, evident from the way foreign fighters in Iraq and Syria emulate and celebrate famous predecessors from the 1990s, such as Ibn Khattab. This is important, as it shows that we are not dealing with disparate phenomena that happen to resemble each other but rather with one and the same movement. Moreover, it suggests that the movement’s existence is not dependent on the features of any one of the host conflicts. To be sure, the size of the various contingents varies by conflict-specific factors — for example, the Syrian war attracted large numbers in part because the rebels initially enjoyed widespread international support — but the movement as a whole transcends individual conflicts. It follows that the phenomenon will likely not disappear with the end of the foreign fighting in Syria. It is likely to reemerge in any new conflict zone that will allow it.

The second insight is the centrality of foreign fighting to jihadism. Byman’s account makes it clear that the history of jihadism is largely the history of jihadi foreign fighting. Road Warriors provides a better overview of the jihadi movement’s history than any book about jihadi international terrorist operations. As important as it is to know the history of the latter, foreign fighting is the rule and international terrorism is the exception as far as the jihadi movement is concerned. The foreign fighter contingents presented in Road Warriors involved an order of magnitude more people than have ever taken part in jihadi terrorist attacks outside conflict zones. Jihadi foreign fighters have also undertaken many more operations and killed more people than have their out-of-theatre comrades.38

Moreover, the movement’s biggest heroes — Azzam, Ibn Khattab, al Zarqawi — are all people who primarily waged asymmetrical warfare in conflict zones. The main exception is Osama bin Laden, but even he had solid foreign fighter credentials before orchestrating the 9/11 attacks. By contrast, those who executed major out-of-theatre attacks, such as Muhammad al Islambouli (1981 Sadat assassination), Muhammad Atta (9/11), or Abdelhamid Abaaoud (2015 Paris attacks) are not treated with nearly the same reverence. This is not to say that the out-of-theatre activities of jihadi groups are insignificant. They are important to international politics, because they have an outsize psychological impact that can make countries go to war (America post-9/11), devastate tourism industries (Egypt after the 1998 Luxor attacks),39 or trigger extreme anti-Muslim policies (China after the Uyghur stabbings in the late 2000s). It is only to say that the jihadi movement depended for its survival on access to conflict zones and foreign fighting seems to be its lifeblood.

The third and related insight is that jihadis have been more successful as foreign fighters than as domestic revolutionaries. All the chapters in Road Warriors take place in wars that jihadis themselves did not start, and several protagonists had a history as failed revolutionaries. In fact, all Sunni Islamist attempts to topple the local government or start an insurgency in a country at peace have failed. In Egypt, militant Islamists periodically made such offensives from the 1950s to the early 1990s, each time without success. In Syria, the uprising of the late 1970s was brutally repressed. In Algeria in the 1990s, the militants held out for slightly longer, but eventually suffered the same fate. Ditto for the al Qaeda offshoot that tried to wage a terrorism campaign in Saudi Arabia in the early 2000s. It is only in areas that have descended into war for other reasons — 1980s Afghanistan, 2000s Iraq, or 2010s Syria — that jihadis have truly thrived. This testifies to the limited popular appeal of jihadism, to the difficulty of mounting revolutions, and to the repressive power of modern technocratic nation-states.

Escaping the Cheese Bell

These three observations buttress a hypothesis about the relationship between foreign fighting and terrorism that I have alluded to in previous writings but not yet articulated in full.40 I call it the Cheese Bell Theory of foreign fighting. It suggests that modern states have become so effective at repressing small rebel groups that the latter only survive if they can periodically leave the area of state control. Foreign fighting is a mechanism for achieving this. Functioning states are like cheese bells in the sense that they crush all minor forms of rebellion inside their jurisdiction. Rebel groups that are caught inside the bell tend to get dismantled, while those that can leave — for example by coming and going as foreign fighters — stand a better chance of survival.

It is useful here to reflect on just how powerful the modern technocratic state has become. Taxation and the legal system allow the state to operate powerful police forces and intelligence services, giving the state an enormous operational advantage vis-a-vis small rebel groups. Technological advancement increases this advantage in the long term, because states have more resources at their disposal and can harness new technology more effectively than can small non-state actors. Moreover, digital technology makes societies more regulated and increases the observability and traceability of economic transactions, interpersonal communications, and individual physical movements. In wealthy modern societies, almost everything we do is recorded and potentially accessible to a capable intelligence service: our purchases (through credit card records); our movements (through surveillance cameras); and of course our phone calls, emails, and internet activity. Even if you try to stick to analogue technologies, such as cash and personal meetings, you can get caught on other people’s mobile cameras, and artificial intelligence may even flag you for not leading a normal, trace-leaving digital life.

Much has been written about the advantages that new technologies confer on terrorist groups and about the opportunities that our increasingly connected societies offer to malicious actors.41 However, a strong argument can be made that these advantages are primarily of a tactical and not strategic nature. In functioning states, new technologies appear to make it easier to carry out single operations, but harder to wage sustained campaigns of violence. If you are a first-time terrorist who is not on the radar of the authorities, you can plan in relative peace and make full use of the opportunities of modern technology. After that first attack, however, the security services come after you, and then it becomes a whole different ballgame — one that modern states, especially the wealthy ones, almost always win.

This argument is supported by two broad patterns in the history of terrorism in the West. The first is that the long trend of terrorist activity — measured in both attacks and casualties — has been steadily declining since the late 1980s.42 The break in the curve is usually attributed to the end of the Cold War, but the late 1980s also marks the beginning of the systematic introduction of information technology in Western state bureaucracies and the widespread societal adoption of digital communications technologies. It is not far-fetched to suggest that terrorism in the West may have declined not only because of the end of the Cold War, but also because the computer, in the broad sense, has empowered intelligence services more than it has terrorist organizations. The second pattern is the virtual disappearance of active terrorist organizations from Western societies. In the 1970s and 1980s, much terrorism was carried out by organizations and these organizations sometimes survived for years, carrying out numerous attacks before being dismantled by police. In the 2000s and 2010s, terrorism — at least the large-scale variety — is perpetrated, to a much larger extent, by cells and individuals as opposed to stable organizations. Running a classical rebel organization — with a leadership, an internal bureaucracy, and some continuity of personnel — has become extremely difficult in Europe and North America. To be sure, violent political organizations still exist, but these are usually organizations that engage in low-level violence and therefore do not attract the full wrath of the modern surveillance state. Groups that perpetrate mass-casualty attacks, on the other hand, tend to get dismantled relatively quickly.

To both of these patterns there is a partial exception, namely jihadi terrorism. While the terrorist activity curve in the West from 1990 to 2020 is generally downhill-pointing, there were temporary surges in activity in the 2000s and 2010s, especially when measured in casualties. Much of this activity was perpetrated by militant Islamists, despite the fact that Western security agencies put most of their counter-terrorism resources into fighting jihadis. The latter thus seemed to defy the forces of repression that were pushing far-right, far-left, and ethnic separatist violence down. Moreover, although jihadis have not been able to run stable organizations inside the West, they have periodically been able to sustain logistical structures there that come close to those of classical organizations. How can we explain this exception? Why has jihadism been so lethal and resilient in the West when other ideological movements have struggled, and when jihadism recruits from a much smaller population (Muslims in the West)?

The Cheese Bell Theory suggests that the answer lies in foreign fighting. For a variety of reasons, jihadis in the West have been willing and able to engage in a lot more foreign fighting than have radicals of other ideological orientations. This has enabled members of jihadi networks to temporarily escape, at least partially, the watchful eye of their countries’ intelligence services, while getting training and forming connections with more experienced militants in conflict zones. This has provided jihadis with what military theorists call “strategic depth,” namely, a distance between the front lines and the home base so large that the enemy cannot reach the rebels’ home base and disturb force production. For example, when foreign fighters are off in faraway places, such as Afghanistan or Syria, it is much harder for European security services to disrupt their training and plotting than if the same activity were taking place in France or Germany. In short, foreign fighting has allowed jihadis to escape the cheese bell.

Meanwhile, most other militant movements in the West — be they the far right, the far left, or radical separatists — have generally not had the same privilege, at least in the past few decades (the Cold War provided more such opportunities for those other group types). There have been exceptions, such as the neo-Nazi foreign fighters in the Ukraine, or the leftist ones fighting with the Kurds against the Islamic State in the mid-2010s, but these activities have not been nearly as long-lived or involved as many people as the foreign fighting of the jihadis. As a result, non-jihadi militants in the West have been stuck inside the cheese bell, living at the mercy of their ever more capable security services.

Similar dynamics have likely also been at play in the Muslim world, although the tools and techniques of state repression have been somewhat different. Until recently, at least, authoritarian regimes have generally relied on more heavy-handed methods and more bulk surveillance of political opponents than have democratic states, but the end result has been the same: a considerable ability to repress and dismantle small rebel groups on their own territory. As a result, jihadi groups operating in Muslim countries at peace have tended to get dismantled relatively quickly, as noted earlier. This tendency is likely to strengthen in the years ahead as non-democratic regimes get access to more advanced surveillance technology while remaining legally unrestrained in the deployment of these technologies.


For jihadis, then, foreign fighting has been more than an ideologically meaningful modus operandi or a series of military adventures. It has been an activity of utmost strategic importance, one that has been crucial to the very survival of the jihadi movement. It is not the only source of the movement’s resilience, but it is arguably one of the principal ones, along with propaganda distribution technologies and the persistence of armed conflicts in the Muslim world. Foreign fighting has been a mechanism for avoiding domestic state repression, and its value for rebels has increased in recent decades as the repressive power of modern technocratic states has grown.

It follows from the Cheese Bell Theory that the jihadi movement will suffer if its opportunities to engage in foreign fighting are reduced in the future. It is probably impossible to completely eliminate jihadi foreign fighting, but it is certainly possible to do more than governments did from the 1980s to the mid-2010s. As Byman notes, countering foreign fighting was generally not a priority in either the West or in the Muslim world prior to the Syrian civil war. In recent years, many countermeasures have been put in place, and Byman offers further suggestions on what to do. Jihadi strategists thus have every reason to be unhappy with the publication of Road Warriors.


Thomas Hegghammer is a senior research fellow at the Norwegian Defence Research Establishment (FFI) in Oslo and the author of The Caravan: Abdallah Azzam and the Rise of Global Jihad (Cambridge, 2020).


4. Tracing the Line of Foreign Fighters Over Time

Aaron Y. Zelin


Over the past decade, research on foreign fighters in the jihadi movement has become ubiquitous. This is due to the unprecedented mobilization of individuals to fight in Syria alongside the Islamic State, al-Qaeda’s Syrian branch,43 and other smaller jihadi groups. The mobilization to Syria was four times larger than the number of foreign fighters who joined the anti-Soviet jihad in Afghanistan. Although there was little scholarship on jihadism, let alone Muslim foreign fighters, in the aftermath of the Afghanistan war, in 1992, Middle East scholar Martin Kramer identified the potential fallout of foreign fighters returning home: “The Arab volunteers began to return home, where they became involved in violent opposition to their own governments.”44 In particular, Kramer notes the cases of the Algerian civil war and the terrorism campaign in Egypt.45 Despite this prescient work on Muslims who travel to fight in foreign conflicts, a phenomenon we have continued to see in the decades since, Daniel Byman’s newest book Road Warriors: Foreign Fighters in the Armies of Jihad is the first comprehensive study that provides a sweeping history of this phenomenon from its infancy in Afghanistan in the 1980s through the most recent call to fight in Syria.

In addition to guiding the reader through key stories of individuals that helped incubate, shape, and carry the banner from one battlefield to the next, Road Warriors is in many respects also a history of the modern global jihadi movement. So much of that movement was born in and has evolved through the test of battle and in dealing with external adversaries as well as internal squabbles over theology, military strategy, and the tactics necessary to bring about jihadis’ desired end goal: a stable caliphate based on their interpretations of Islam that eventually grows to rule over the entire globe.

Although more researchers and government officials are paying attention to the foreign fighter phenomenon on a consistent and serious basis in comparison to the early 1990s, Byman contends that “the threat posed by jihadist foreign fighters is large and growing.”46 This is in part because each mobilization has built upon previous ones: “Foreign fighters learned and integrated strategies from their predecessors and then inspired their successors. … [J]ihadism is vibrant and resilient, whether you look just at terrorism or also civil wars and the spread of their ideology.”47

Byman rightly assesses that governments have adapted to the challenge of foreign fighters by using more sophisticated tools to combat the mobilizations related to them. At the end of Road Warriors, there is a chapter on solutions to the question of foreign fighters based on what has been learned in the past few decades, as well as best practices for how to interdict and prevent individuals in five different stages of potential mobilization from becoming a foreign fighter.48

And although the academic community has come to a greater understanding of the broader dynamics related to jihadi foreign fighting in the past decade, challenges remain in terms of whether politicians will truly internalize the lessons they’ve learned or whether the broader public will accept that a 100 percent success rate in dealing with terrorism is unlikely. These challenges are compounded by the rise of far-right politics in the West and oversimplistic responses that conflate everyday Muslim practice with violent jihadism.49 These responses have led to a culture war in Europe in particular that could breed the type of sectarianism that groups like the Islamic State feed off of as they pursue their goal of eliminating the so-called “gray-zone.”50 Therefore, as Byman rightly points out, in this regard, as in the medical field, Western leaders should “at least do no harm.”51 As for the general public, “a culture of resilience would help” too.52

Common Threads

One of the greatest strengths of Byman’s book is that it brings to the fore the similar dynamics that have been at play over and over again in various foreign fighting fronts. One of these is the phenomenon of countries like Pakistan, Syria, and Turkey that neighbor a particular conflict overtly enabling support or turning a blind eye to facilitation and logistics networks running through their country.53 I noticed many of these trends in research for my book Your Sons Are At Your Service: Tunisia’s Missionaries of Jihad, which is the first comprehensive history of the Tunisian jihadi movement.54

According to Byman, in the aftermath of the anti-Soviet jihad, “some Arab Afghans had their passports revoked by their home countries or risked arrest on their return and thus had nowhere to go.”55 This created what he describes as a “a professional jihadi not tied to one particular struggle” that began to play out a few years later in Bosnia.56 In the case of Tunisia, around 400 individuals went to Afghanistan between 1979 and 1992.57 However, the Bosnian conflict is what crystallized the movement. Some 100 Tunisians died in Afghanistan. The 300 who survived could not return to Tunisia or they would have been arrested. Instead, some of them sought asylum in Europe and either became enmeshed in jihadi support, facilitation, logistics, and forgery networks in Milan, Brussels, Paris, and London, or ended up going to join Katibat al-Mujahidin in Bosnia.58 The connections made through this diaspora network provided the backbone for what became the Tunisian Combatant Group in the late 1990s. This group planned and executed the assassination of Afghan Northern Alliance leader Ahmad Shah Masud two days before 9/11.59 A number of leaders in the Tunisian Combatant Group would then go on to found and lead Ansar al-Sharia in Tunisia — a pro-al-Qaeda group that was active in Tunisia from 2011 to 2013 — after the 2011 Tunisian revolution.

This illustrates the residual effects of networks as well as the poor policies that have effectively made individuals stateless, leaving them without any recourse other than to remain engaged and active within the jihadi movement. We have seen this play out in other cases like Algeria, Libya, and Egypt, as Byman highlights. Now, governments are stripping the citizenship of foreign fighters who have gone to northeast Syria or are not repatriating them.60 Although the second- and third-order effects of this cannot immediately be known, if history is any indicator, these foreign fighters will not just be a random footnote, given that alumni of the anti-Soviet jihad continue to play a role in the jihadi movement today. Consider also that there are far more surviving foreign fighters from the Syrian jihad than from the one in Afghanistan. And unlike back then, when the broader movement was starting from scratch, today’s foreign fighters have decades of experience to build off of and robust networks to rely upon. This latter point about networks, alongside increased ease of travel and expanded communication technologies, is important because it helps explain the expansion of foreign fighter networks in the past decade that facilitated the large number of fighters going to Syria in particular.61

The case of Ansar al-Sharia in Tunisia also helps underscore a pattern that has helped incubate these mobilizations. Byman demonstrates that, over time, so-called jihadi feeder groups have benefited from being based primarily in democratic countries where they can take advantage of the greater freedoms. These countries have given the groups the space to recruit individuals legally and to push the limits of free speech. These recruiters have, in many cases, incited individuals to become foreign fighters.62

Similar to al-Muhajirun in the United Kingdom, Sharia4Belgium, Revolution Muslim in the United States, and other similar organizations in the West, Ansar al-Sharia in Tunisia preached and provided social services openly in Tunisia for the two-and-a-half year period following the Tunisian revolution. The leader of the group, Abu Iyadh al-Tunisi, also promoted the idea of fighting abroad even if the group was focused on doing dawa (proselytization) locally. In 2011, Abu Iyadh argued,

jihad actually just now began in Iraq because the Americans left behind their bags to the Persians and the rawafidh (rejectionists) to control Iraq. . . . You say to me that the American occupation ended? And I say to you that this occupation left the enemies of the umma (nation) such as the majus [Iran] and the rawafidh selling the umma to the West. My brother, jihad is necessary now, and it is necessary that [then Iraqi Prime Minister Nouri] al-Maliki and his cronies be eradicated from the face of the earth, and the mujahidin in Iraq should escalate their attacks. . . . We ask God to help our brothers to succeed.63

Because Ansar al-Sharia in Tunisia was able to freely recruit individuals locally in Tunisia, when the Tunisian government began to crackdown on it in 2013, there was a greater population of potential individuals that could then be recruited for foreign fighting in Syria.

Byman also highlights the phenomenon of local governments not taking the outflow of foreign fighters seriously.64 In Tunisia, even though the government was aware of the potential blowback, there was little done when Tunisians began to mobilize to Libya and Syria in the first couple of years after 2011. For example, Tunisian Interior Minister Ali Larayedh said at the time, “I understand the situation well, and I understand the problems it will cause in the future when the Syrian brothers’ ordeal ends.”65 Tunisian President Moncef Marzuki echoed these concerns: “Experience has taught us of the consequences when these fighters give money and arms return to their countries.”66 However, Larayedh explained that “we cannot legally prevent a citizen from leaving the country if he says he is leaving for work or tourism.”67 This would change only beginning in late spring 2014.

But why do individuals go to fight in the first place? According to Byman, “fighters used faith, not socioeconomic marginalization to explain their decisions,”68 especially in the case of Syria. In my research on the Tunisian jihadi movement, I found that there were many reasons that individuals went to fight in Syria: altruism, anti-colonial sentiment, bandwagon effect, disillusionment, economic opportunity, establishment of the caliphate, impressionability, the ability to openly recruit there, personal tragedy, prison radicalization, recidivism, desire for redemption, using religion to fill a void, and sectarianism.69 The most commonly given reasons were disillusionment with the Tunisian revolution, the Islamic State’s establishment of its caliphate, and a desire for redemption after being involved in criminality or perceived sins.

Once in the warzone, local populations that originally accepted foreign fighters’ help turn on them due to their more extreme vision and lack of local understanding. As Byman explains, “this would prove a pattern: locals welcomed foreigners when they were supporting the local fight against a perceived oppressor, but this welcome turned to bitterness when the foreigners tried to take over and become a threat in their own right.”70 Tunisian fighters and volunteers who joined the Islamic State were viewed by local Syrians as some of the most extreme elements.71 About the Tunisians in al-Raqqah, one Syrian remarked that they were “high on other people’s fears.”72

Byman’s book provides key guide posts for understanding the processes that have led to foreign fighter mobilizations in the past. Whether world governments learn from this or continue to fail to mitigate this phenomenon over and over again is another story. Whatever happens in the future, Road Warriors is an important piece of scholarship that should be on the bookshelf of academics, practitioners, and policymakers alike.


Aaron Y. Zelin is the Richard Borow Fellow at the Washington Institute for Near East Policy, a Visiting Research Scholar at Brandeis University, and Founder of He is the author of the recently released book Your Sons Are At Your Service: Tunisia’s Missionaries of Jihad (Columbia University Press, 2020).


Image: Erwin Franzen (CC BY-NC-SA 2.0)


1 “The United Nations Global Counter-Terrorism Strategy: Seventh Review,” United Nations General Assembly, June 30, 2021,

2 “IntelBrief: United to Fight Terrorism? Reviewing the UN’s Global Counterterrorism Strategy,” The Soufan Center, May 6, 2021,

3 “Greater Cooperation Needed to Tackle Danger Posed by Returning Foreign Fighters, Head of Counter‑Terrorism Office Tells Security Council,” United Nations, Nov. 28, 2017,

4 “Letter dated 21 January 2021 from the Chair of the Security Council Committee pursuant to resolutions 1267 (1999), 1989 (2011) and 2253 (2015) concerning Islamic State in Iraq and the Levant (Da’esh), Al-Qaida and associated individuals, groups, undertakings and entities addressed to the President of the Security Council,” United Nations,

5 Daniel Byman, Road Warriors: Foreign Fighters in the Armies of Jihad (New York: Oxford University Press, 2019), 7.

6 On Shiite foreign fighters see, R. Kim Cragin, “Semi Proxy Wars and U.S. Counterterrorism Strategy,” Studies in Conflict and Terrorism 38, no. 5, (March 2015): 311–27, On white identity extremists see, White Supremacy Extremism: The Transnational Rise of the Violent White Supremacist Movement, The Soufan Center, September 2019,

7 Byman, Road Warriors, 41.

8 Daniel Byman, Road Warriors: Foreign Fighters in the Armies of Jihad (New York: Oxford University Press, 2019), 7.

9 R. Kim Cragin, “Semi Proxy Wars and U.S. Counterterrorism Strategy,” Studies in Conflict and Terrorism 38, no. 5 (March 2015): 311–27,

10 Byman, Road Warriors, 8.

11 R. Kim Cragin, “An Early History of al-Qa’ida,” The Historical Journal 51, no. 4 (December 2008),

12 Abdullah Azzam, In Defense of Muslim Lands, unpublished manuscript, est. 1984,

13 Abdullah Anas, To the Mountains: My Life in Jihad from Algeria to Afghanistan (London: Hurst Publishers, 2019); and Mustafa Hamid, “Chatter from the Top of the World,” unpublished manuscript(s), est. 1992,

14 R. Kim Cragin and Susan Stipanovich, “Metastases: Exploring the Impact of Foreign Fighters in Conflicts Abroad,” Journal of Strategic Studies 42, nos. 3-4 (November 2017),

15 Byman, Road Warriors, 53.

16 R. Kim Cragin, “Metastases.”

17 R. Kim Cragin, “Metastases.”

18 Byman, Road Warriors, 103–24.

19 Jean-Charles Brisard, Zarqawi: The New Face of al-Qaeda (New York: Other Press, 2005), 93; Ahmed Rashid, Descent Into Chaos: The U.S. and the Disaster in Pakistan, Afghanistan, and Central Asia (New York: Penguin Books, 2009), 282; and Jason Burke, The 9/11 Wars (London: Penguin Books, 2011), 165.

20 Byman, Road Warriors, 108.

21 R. Kim Cragin, “Metastases.”

22 R. Kim Cragin, “Metastases.”

23 Byman, Road Warriors, 117–25.

24 Byman, Road Warriors, 164; and R. Kim Cragin and Phillip Padilla, “Old Becomes New Again: Kidnappings by Daesh and Other Salafi Jihadists in the 21st Century,” Studies in Conflict and Terrorism 40, no. 8, November 2016,

25 Alexander Meleagrou-Hitchens and Seamus Hughes, “The Threat to the United States by the Islamic State’s Virtual Entrepreneurs,” CTC Sentinel 10, no, 3, (March 2017),

26 “The Repatriation of ISIS-affiliated Women,” CTED Analytical Brief, United Nations, September 2019,

27 R. Kim Cragin, “The Challenge of Foreign Fighter Returnees,” Journal of Contemporary Criminal Justice 33, no. 3, (April 2017),

28 Byman, Road Warriors, 209.

29 R. Kim Cragin, “The Challenge of Foreign Fighter Returnees.”

30 R. Kim Cragin, “The Enemy Gets a Vote,” Lawfare Blog, Sept. 16, 2018,

31 “U.N. Security Council Resolution 2178,” Sept. 24 2014, (2014).

32 For a comprehensive bibliography, see Judith Tinnes, “Bibliography: Foreign Terrorist Fighters,” Perspectives on Terrorism 12, no. 5 (2018): 121–59,

33 See, e.g., Lorne Dawson, “A Comparative Analysis of the Data on Western Foreign Fighters in Syria and Iraq: Who Went and Why?” ICCT Research Paper, The Hague February 2021.

34 See, e.g. Edwin Bakker and Roel de Bont, “Belgian and Dutch Jihadist Foreign Fighters (2012–2015): Characteristics, Motivations, and Roles in the War in Syria and Iraq,” Small Wars and Insurgencies 27, no. 5 (2016): 837–57,; and Ben Rich and Dara Conduit, “The Impact of Jihadist Foreign Fighters on Indigenous Secular-Nationalist Causes: Contrasting Chechnya and Syria,” Studies in Conflict and Terrorism 38, no. 2 (2015): 113–31,

35 See, e.g., David Malet and Rachel Hayes, “Foreign Fighter Returnees: An Indefinite Threat?” Terrorism and Political Violence 32 no. 8 (2020): 1617–35,

36 See, e.g., Arkadiusz Legiec, “Profiling Foreign Fighters in Eastern Ukraine: A Theoretical Introduction,” in Not Only Syria? The Phenomenon of Foreign Fighters in a Comparative Perspective, ed. Kacper Rekawek (Amsterdam: IOS Press, 2017), 22–30; Jesse C. Reiff, “When Ali Comes Marching Home: Shi’a Foreign Fighters after Syria,” Studies in Conflict and Terrorism 43, no. 11 (2020): 989–1010,; and Ariel Koch, “The Non-Jihadi Foreign Fighters: Western Right-Wing and Left-Wing Extremists in Syria,” Terrorism and Political Violence 33, no. 4 (2021): 669–96,

37 Thomas Hegghammer, The Caravan: Abdallah Azzam and the Rise of Global Jihad (Cambridge: Cambridge University Press, 2020), 51.

38 In the West, Islamist foreign fighters have historically outnumbered local Islamist attackers by at least an order of magnitude. See Thomas Hegghammer, “Should I Stay or Should I Go? Explaining Variation in Western Jihadists’ Choice Between Domestic and Foreign Fighting,” American Political Science Review 107, no. 1 (February 2013): 1–15, Moreover, the number of violent incidents in the conflict zones where Islamist foreign fighters have tended to join has been several orders of magnitude larger than that observed in Western countries. See, e.g., the Global Terrorism Database,, or the UCDP/PRIO Armed Conflict Dataset,

39 See, e.g., David Fielding and Anja Shortland, “How Do Tourists React to Political Violence? An Empirical Analysis of Tourism in Egypt,” Deutsches Institut für Wirtschaftsforschung Discussion Papers 1022 (2010),

40 See, e.g., Thomas Hegghammer, “The Future of Jihadism in Europe: A Pessimistic View,” Perspectives on Terrorism 10, no. 6 (2016): 162,

41 See, e.g., Maura Conway, et al., eds., Terrorists' Use of the Internet (Amsterdam: IOS Press, 2017).

42 See the Global Terrorism Database,

43 At first, Jabhat al-Nusrah and then later Huras al-Din.

44 Martin Kramer, “The Global Village of Islam,” Middle East Contemporary Survey, Vol. 16: 1992 (Boulder and Oxford: Westview, 1994), 196.

45 Kramer, “The Global Village of Islam,” 197–98.

46 Daniel Byman, Road Warriors: Foreign Fighters in the Armies of Jihad (Oxford: Oxford University Press, 2019), 8.

47 Byman, Road Warriors, 249.

48 Byman, Road Warriors, 252–63.

49 Jocelyne Cesari, “Securitization of Islam and Religious Freedom,” Berkley Center for Religion, Peace & World Affairs, Sept. 13, 2018,

50 Byman, Road Warriors, 214; and, Dabiq Magazine, Issue 7, The Islamic State, al-Hayat Media, February 2015, 54–67,

51 Byman, Road Warriors, 267.

52 Byman, Road Warriors, 266.

53 Byman, Road Warriors, 13.

54 Aaron Y. Zelin, Your Sons Are at Your Service: Tunisia’s Missionaries of Jihad (New York: Columbia University Press, 2020).

55 Byman, Road Warriors, 35.

56 Byman, Road Warrior, 41.

57 Zelin, Your Sons Are at Your Service, 43.

58 Zelin, Your Sons Are at Your Service, 47–51.

59 Zelin, Your Sons Are at Your Service, 57–61.

60 Maarten P. Bolhuis and Joris van Wijk, “Citizenship Deprivation as a Counterterrorism Measure in Europe: Possible Follow-Up Scenarios, Human Rights Infringements and the Effect on Counterterrorism,” European Journal of Migration and Law 22, no. 3, 338–65,

61 Byman, Road Warriors, 10.

62 Byman, Road Warriors, 15.

63 Zelin, Your Sons Are at Your Service, 179.

64 Byman, Road Warriors, 17.

65 Zelin, Your Sons Are at Your Service, 180.

66 Zelin, Your Sons Are at Your Service.

67 Zelin, Your Sons Are at Your Service.

68 Byman, Road Warriors., 172.

69 Zelin, Your Sons Are At Your Service, 218.

70 Byman, Road Warriors, 115.

71 Zelin, Your Sons Are At Your Service, 194.

72 Zelin, Your Sons Are at Your Service, 195.