“The youngest terrorist suspect ever” was the headline in the Dutch De Telegraaf newspaper on 16 September 2015. Rahma E., a Dutch Somali-born girl, fifteen years old, living with her mother in Maastricht, was arrested for preparing to emigrate to the IS Caliphate in Syria to join the international jihad. She was arrested in possession of a new phone with Syrian telephone numbers and a travel itinerary, after having chatted extensively about her plans with a sister-in-arms and after sending her a gold ring as payment for her trip. Interestingly, in his verdict, the judge made a clear distinction between the different stages of preparation. Rahma E. had made preparations with respect to planning her trip to Syria to join IS; this constituted planning to commit a crime (joining a terrorist organization). But since she had not actually started her trip, she was acquitted of having taken specific action, such as initiating the journey. The verdict implied that, had she actually left the country, this would have been considered an attempt to join a terrorist organization – a departure from previous rulings that acquitted passport-carrying Dutch suspects from the same crime who were caught as far away as Turkey.

A fifteen-year-old girl triggering a stream of serious legal debate involving all kinds of novel legal arguments and sending a shudder of media-induced horror through society – this would have been unthinkable in the Netherlands in the 1970s. Back then, a handful of radical Dutch students really did arrive in Yemen, to train with Palestinian terrorist organizations alongside members of the Red Army Faction. Upon their return, they were not – and could not have been (in the absence of any terrorism law) – prosecuted. They were “merely” closely monitored by the secret service and ridiculed in public. They were not considered terrorists, nor were they defined as foreign fighters or foreign volunteers. How times have changed. A spate of jihadist attacks and the ensuing “power of nightmares” (Adam Curtis)Footnote ¹ since 2001 has enabled the implementation of a series of new and far-reaching terrorism laws – with the latest legislative proposal in the Netherlands (September 2019) aiming to penalize even merely staying in a so-called terrorist area.

We have seen an unstoppable flood of books on radicalization and terrorism by academics and policy experts alike. Yet, serious, empirically grounded studies on the crucial, adjacent field of “foreign fighters” are rare. It is the great achievement of the Leeds-based historian Nir Arielli to start not with the problem of terrorism, but to put the question of transnational war volunteers centre stage. “What makes people fight and risk their lives for countries other than their own?”, he wonders. And “Why do people volunteer for foreign causes?”.

Instead of crafting a response around various models and theories of radicalization, Arielli does three things. First, he proposes to resituate this question where it belongs: not with invented, postulated, and alleged general “root causes” or psychopathological individual mechanisms of alienation and traumatization, but as a historical concept that is being attributed to some people in some instances – and sometimes not even considered at all. Second, he makes the case for how the phenomenon of foreign fighters can be properly understood only by researching it in conjunction with the emergence of the nation state. In the case of the fifteen-year-old girl mentioned above, we might wonder whether she would have been prosecuted as a potential terrorist without a historical context that posits “the Caliphate” as an international threat to our national security. And thirdly, what this book really aims to do is to historicize the question of foreign fighters. It unpacks how foreign fighters were perceived “differently by different people in different historical contexts”. This is not a platitude intended to diminish the problem of violent conflict, or the lethal potential mobilized by such foreign fighters. What Arielli painstakingly tries to do is to dissect the epitaph “foreign fighters” from the question of “terrorism”. Terrorism is such a pejorative concept, and so much subjected to normative interpretations and legal judgements, that it is very hard to produce an “objectified” historical narrative of its development. With foreign fighters, Arielli tries to demonstrate, it is less difficult to “avoid passing judgment” and instead reconstruct the trajectory of the terminology of “foreign volunteers” (a more apt, neutral description, he argues, than “fighters”) and its usage since the eighteenth century.

Does Arielli succeed in creating a new master narrative of the phenomenon of foreign volunteers? Yes. He makes important inroads in this direction. He informatively historicizes the occurrences in history of nationals of one country volunteering to fight abroad. Commencing with the French Revolutionary Wars and the absorption of national conscripts as well as foreign volunteers into the French Grande Armée, he shows how fighting for a foreign king – a standard practice up until the eighteenth century – gradually became seen as a security breach, as a liability to the rise of new nation states and standing conscript armies, and even as a capital offence. (On his return in 1813, the Dutch king Willem I made it a capital offence for Dutch soldiers to remain enlisted in Bonaparte's army.) With military service becoming more respectable and more seminal to the creation and maintenance of a viable nation state, foreign fighters increasingly became a problem – a military one, but also, and even more so, a challenge to public morals and national identity. Fighting in a foreign army was regarded as treason, and several laws in that respect were formulated for the first time in the early nineteenth century.

Where Arielli is less convincing – I would have loved to read more about this – is with respect to his “wave theory” in relation to foreign volunteers – a theory that parallels David Rapoport's theory on waves of terrorism.Footnote ² If the French Revolutionary Wars triggered a first wave of foreign volunteers – and the corresponding attempts to penalize them – why jump to the October Revolution of 1917 and propose a “second wave” of left-wing versus right-wing volunteers only then? Was there nothing in between? Arielli postulates this second wave only in passing (p. 39) and neither explains nor expounds on this any further beyond a single paragraph. An alleged “third wave” of volunteers “bound together under the banner of a clash of civilizations” is left equally unclarified. If the rise of the nation state, including its increasing ideological positioning in a global clash of civilizations, forms the backdrop to the “foreign volunteers” phenomenon, then the link between national identity and ideological transnational volunteering could and should have been further specified. Are the waves ideologically defined, or should they be seen as global convulsions of political dissent – people running away to fight for liberty elsewhere?

Yet, there might even be another explanation or driver behind the waves that is omitted altogether. Strangely, Arielli does not touch upon socio-economic questions or motives behind the foreign volunteering. For example, many of the more than 3,000 Dutchmen who, between 1866 and 1870, fought in defence of the Papal States, were recruited by priests who were easily able to convince boys from poorer and deprived backgrounds to join the Zouave forces. Apart from earning themselves or their relatives credit in heaven, they were looking for adventure, to travel abroad, and to find for themselves and their poor Catholic families a livelihood and a pension. A personal quest for significance, a spiritual attempt to attain redemption, or a contribution to the metaphysical battle against evil – motives that Arielli rightly identifies among the cohorts of volunteers – were oftentimes married with more mundane socio-economic push and pull factors. This is not to suggest we raise from academic death another “root cause” discussion on transnational volunteers, but to make a case for a more nuanced and empirically grounded historical assessment of foreign fighters. One is more likely to look abroad for meaning and ideological relevance when the nation state one belongs to closes its shutters and leaves so many young men or women in the cold, destitute, without a job, or without a political and social home.

Moreover, this possibility – of finding both spiritual meaning and an economic livelihood abroad – does not often happen spontaneously. Oftentimes, recruiters, groups, organizations, and caliphates are proactively busy spying, prying, luring vulnerable youths into their rank and file. Many a Papal, communist, or jihadist foreign fighter would be drawn in with the promise not just of transcendental bliss in the long run, but very real, concrete remuneration and job opportunities in the here and now. As one foreign fighter from the Netherlands, recruited by IS, put it, he would rather race a four-wheel drive through the desert in Syria than restock shelves at the Aldi supermarket. Interestingly, in his recent monograph on why people radicalize, Kees van den Bos has made a persuasive argument for how processes of radicalization and the willingness to enter into battle or violent conflict for one's convictions can be propelled by feelings of injustice.Footnote ³ Such “injustice frames” are frequently manufactured and augmented by foreign recruiters and transmitted on the internet. They can be considered the missing socio-psychological link between ideology, real or perceived economic plight (or solidarity with the plight of others), and proneness to violence.

Arielli's book is the first highly readable and instructive attempt by a historian to draw a master narrative of foreign volunteers through history, sketching “links in a chain” that span from Byron, via Garibaldi, the International Brigades, the Condor Legion, to bin Laden. The next step, however, requires a far more systematic grounding and chronological investigation of the different volunteer waves, their connections, and transfers. Did volunteers from earlier waves pass on their knowledge to future ones? Did transnational volunteering indeed wax and wane with marked transformations in the nation state and the integration (or exclusion) of certain groups? Is it possible to make a serious assessment of the socio-economic background of these volunteers or identify their recruiters? Only then can we really start to understand the phenomenon of transnational volunteers as something distinct in history, rather than a series of gripping anecdotes and microhistories. Only then can we start to think about how the declining nation states of the twenty-first century can deal with young people who find a “just cause” in fighting abroad.