Expert Commentary

Western jihadists returning to home countries? What past empirical data tell us

Data and research published in American Political Science Review relating to the period 1990-2010, when the West saw an estimated 1,000 persons become Islamist foreign fighters.

The challenge of dealing with foreign fighters who have left Western countries for the Middle East and beyond continues to trouble policymakers, who fear that the improved fighting skills and accelerated radicalization produced in conflict zones will ultimately result in lethal violence in the homeland. An estimated 100 people from the United States have joined various groups in the Syrian civil war, according to the Congressional Research Service, although to date there have not been public reports of fighters returning. For Europe, the problem is far larger, as in 2012 alone EU nations were already seeing between 700 and 1,400 people flowing into the Syrian fight, where the terrorist group ISIS, or ISIL, continues to sow chaos.

Countries such as Britain are watching and tracking these flows with great concern, and King’s College London ICSR researchers have been profiling those who have left the United Kingdom to fight in Syria and who are now on social media. Researchers at the International Counter-Terrorism Centre at the Hague, among others, have likewise been analyzing the policy and legal challenges in dealing with these foreign fighters; and the RAND Corporation has looked at how to reduce the threat in America. Now, more than 1,000 fighters a month may be joining the battles in Syria. While the ICSR at King’s College London estimated there were 11,000 foreign fighters in Syria as of December 2013, the Washington Post cites U.S. intelligence officials who put the total estimate of foreign fighters at perhaps 16,000 as of October 2014.

Although a May 2014 incident at the Jewish Museum in Brussels was the first known instance in the West of “spillover” from Syria, potential large-scale “blowback” has yet to be seen in the West, even as air strikes have targeted ISIS. And it remains the case that 80% of the fatalities from terrorist acts — an estimated 18,000 in 2013 — took place in just five countries: Afghanistan, Iraq, Nigeria, Pakistan and Syria. But the example of the mujahideen in Afghanistan in the 1980s — the deep historical roots of the 9/11 attacks — remains salient, and in September 2014 President Obama chaired a United Nations Security Council meeting about this developing transnational problem that could prove a massive future liability.

What does the best empirical research suggest about what we might expect in the coming years, as the current conflicts potentially “boomerang”? In a 2013 research paper published in the American Political Science Review, “Should I Stay or Should I Go? Explaining Variation in Western Jihadists’ Choice between Domestic and Foreign Fighting,” Thomas Hegghammer from the Norwegian Defense Research Establishment explores open-source data to examine patterns of Islamist attack plots and plotters in the West. The study estimates certain key metrics: theaters of conflict and participation; domestic or foreign origins of plots; foreign fighter return rates; and returnee impact on domestic terrorist activity. The author focuses on jihadists from North America, Western Europe and Australia between 1990 and 2010, and intends to answer the question of why some western jihadists attack at home while others join insurgencies in places like Afghanistan or Somalia.

The study’s findings include:

  • Between 1990 and 2010, there were 401 plotters in the West, 107 (27%) of whom were previously fighters abroad. Thus, 294 were purely domestic fighters, i.e., those who were prepared to proceed directly to domestic attacks without going abroad first.
  • The supply of Islamist foreign fighters from the West between 1990 and 2010 could be estimated at 945 individuals. This is a “very conservative” estimate, however, and the number could be as high as 7,500.
  • The supply of foreign fighters has been larger than that of domestic fighters at a ratio of at least 3:1 (945 versus 294). Assuming the high estimate (7,500), though, means the maximum ratio could be 25:1.
  • Despite increasing government monitoring and control of such activities, the supply of both domestic and foreign fighters appears to have increased from the 1990s to the 2000s. Most of the increase seems to have occurred in Europe, not in the United States, where the combined domestic-foreign fighter supply stayed roughly the same.
  • One in nine foreign fighters returned to perpetrate attacks in the West after being abroad (107 returnees). In terms of why foreign fighters return for an attack if they originally decided it was preferable to leave, the author proposes two mechanisms: enlistment (“a trajectory in which the foreign fighter is drawn into domestic fighting by a calculating second party”); and “socialization” (when the foreign fighter’s preferences change through the experience of conflict abroad).
  • Overall, foreign fighting is perceived as more legitimate than domestic fighting. As a result, Western jihadists were, all else equal, more likely to join “a distant war zone” than attack at home. The author suggests three hypotheses to explain the prevalence of foreign fighters: opportunity (because it’s easier); training (because training is better and intense abroad); and norms (because there is a preference for it). Hegghammer explains that the first two hypotheses are instrumental and unlikely in light of the available data. The norms hypothesis emerges as the strongest explanation for the prevalence of foreign fighters for several reasons, including the portrayal of recruitment videos with imagery drawn from conflict zones.
  • The presence of foreign fighter returnees increases the effectiveness of attacks in the West: Among the 106 known plots, 49 involved a veteran of a foreign conflict (46%), but these plots were more likely to be executed (58% versus 42% without a foreign fighter involved) and lethal.
  • The author suggests that, even if foreign fighting has become more difficult and more religious leaders increasingly encourage domestic fighting, the preference for engaging in fighting abroad remains strong.

“The tentative data presented here indicate that most prefer to fight outside the West and that most foreign fighters do not ‘come home to roost,’ Hegghammer concludes. “However, the data also point to a veteran effect that makes returnees significantly more effective operatives.”


Keywords: Middle East, terrorism, Islamic State of Iraq and the Levant, ISIL, ISIS

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