Helping or hurting? The impact of foreign fighters on militant group behavior

ABSTRACT

How do foreign fighters affect militant group behavior? Recent studies have examined the impact of foreign fighters on broader conflict outcomes, but we explore their specific impact on group behavior. Using foreign fighter data, we find that the presence of foreign fighters is positively related to group longevity, use of suicide operations, and the geographic spread of its operations. We elaborate on these findings in a case study of foreign fighters in al-Shabaab. This article provides important contributions to both scholarship and policy, elucidating the ideological and logistical impact of foreign fighters on tactics, target choices, and group lifespan.

KEYWORDS:

• Foreign fighters
• terrorism
• militants groups
• insurgency

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

The data supporting the results presented in the paper can be found at https://danieljmilton.wordpress.com/.

Supplementary material

Supplemental data for this article can be accessed here.

Notes

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² David Malet, Foreign Fighters: Transnational Identity in Civil Conflicts (Oxford: Oxford University Press 2013).

³ Barak Mendelsohn, ‘Foreign Fighters – Recent Trends’, Orbis 55/2 (2011), 189–202.

⁴ Thomas Hegghammer, ‘Should I Stay or Should I Go? Explaining Variation in Western Jihadists’ Choice between Domestic and Foreign Fighting’, The American Political Science Review 107/1 (February 2013), 1–15; Thomas Hegghammer, ‘The Rise of Muslim Foreign Fighters: Islam and the Globalization of Jihad’, International Security 35/3 (2010), 53–94; Nir Arielli, From Byron to Bin Laden: A History of Foreign War Volunteers (Cambridge, Massachusetts: Harvard University Press, 2017).

⁵ Mendelsohn, ‘Foreign Fighters – Recent Trends’.

⁶ Randy Borum and Robert Fein, ‘The Psychology of Foreign Fighters’, Studies in Conflict & Terrorism 40/3 (2017), 248–66; Lorne L. Dawson and Amarnath Amarasingam, ‘Talking to Foreign Fighters: Insights into the Motivations for Hijrah to Syria and Iraq’, Studies in Conflict & Terrorism 40/3 (2017), 191–210.

⁷ Borum and Fein, ‘The Psychology of Foreign Fighters’; Dawson and Amarasingam, ‘Talking to Foreign Fighters’; Meirav Mishali-Ram, ‘Foreign Fighters and Transnational Jihad in Syria’, Studies in Conflict & Terrorism 41/3 (2018), 169–190; Sean C. Reynolds and Mohammed M. Hafez, ‘Social Network Analysis of German Foreign Fighters in Syria and Iraq’, Terrorism and Political Violence 31/4 (2019) 661–686; Marco Nilsson, ‘Foreign Fighters and the Radicalization of Local Jihad: Interview Evidence from Swedish Jihadists’, Studies in Conflict & Terrorism 38/5 (2015), 343–58; 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 & Insurgencies 27/5 (2016), 837–57; Christopher Hewitt and Jessica Kelley-Moore, ‘Foreign Fighters in Iraq: A Cross-National Analysis of Jihadism’, Terrorism and Political Violence 21/2 (2009), 211–220; Mohammed Masbah, Moroccan Foreign Fighters: Evolution of a Phenomenon, Promotive Factors, and the Limits of Hardline Policies, SWP Comments 46 (Berlin, 2015); Mendelsohn, ‘Foreign Fighters – Recent Trends’.

⁸ Hewitt and Kelley-Moore, ‘Foreign Fighters in Iraq’; Mohammed M. Hafez, ‘Jihad after Iraq: Lessons from the Arab Afghans’, Studies in Conflict & Terrorism 32/2 (2009), 73–94; Hewitt and Kelley-Moore, ‘Foreign Fighters in Iraq’; R. Kim Cragin and Susan Stipanovich, ‘Metastases: Exploring the Impact of Foreign Fighters in Conflicts Abroad’, Journal of Strategic Studies 42/3–4 (2017), 395–424.

⁹ Hegghammer, ‘The Rise of Muslim Foreign Fighters’.

¹⁰ Thomas Francis Lynch, The Return of Foreign Fighters to Central Asia: Implications for U.S. Counterterrorism Policy, Institute for National Strategic Studies Strategic Perspectives/21 (Washington, D.C: National Defense University Press 2016); Phil Gurski, Western Foreign Fighters: The Threat to Homeland and International Security (Lanham: Rowman & Littlefield 2017); Hegghammer, ‘Should I Stay or Should I Go?’; Arsla Jawaid, ‘From Foreign Fighters to Returnees: The Challenges of Rehabilitation and Reintegration Policies’, Journal of Peacebuilding & Development 12/2 (2017), 102–7; Lorenzo Vidino, ‘European Foreign Fighters in Syria: Dynamics and Responses’, European View 13/2 (2014), 217–24; Daniel Byman and Jeremy Shapiro, ‘Be Afraid. Be A Little Afraid: The Threat of Terrorism from Western Foreign Fighters in Syria and Iraq’, Brookings Policy Paper 34 (2014).

¹¹ Mendelsohn, ‘Foreign Fighters – Recent Trends’.

¹² Kristin M. Bakke, ‘Help Wanted?: The Mixed Record of Foreign Fighters in Domestic Insurgencies’, International Security 38/4 (2014), 150–87.

¹³ Ben Rich and Dara Conduit, ‘The Impact of Jihadist Foreign Fighters on Indigenous Secular-Nationalist Causes: Contrasting Chechnya and Syria’, Studies in Conflict & Terrorism 38/2 (2015), 113–31.

¹⁴ Malet, Foreign Fighters, 4–6.

¹⁵ Malet, Foreign Fighters, 59.

¹⁶ Tiffany S. Chu and Alex Braithwaite, ‘The Impact of Foreign Fighters on Civil Conflict Outcomes’, Research & Politics 4/3 (2017), 1–7.

¹⁷ Arielli, From Byron to Bin Laden, 152–53.

¹⁸ Brian Guy Williams, ‘On the Trail of the “Lions of Islam”: Foreign Fighters in Afghanistan and Pakistan, 1980–2010’, Orbis 55/2 (2011), 216–239.

¹⁹ Peter Krause, ‘The Structure of Success: How the Internal Distribution of Power Drives Armed Group Behavior and National Movement Effectiveness’, International Security 38/3 (2013), 72–116.

²⁰ Daniel Byman, Road Warriors: Foreign Fighters in the Armies of Jihad (New York: Oxford University Press 2019), 12.

²¹ Tyler Evans, Daniel J. Milton, and Joseph K. Young. ‘Choosing to Fight, Choosing to Die: Examining How ISIS Foreign Fighters Select Their Operational Roles’. International Studies Review (2020).

²² Brian Glyn Williams. ‘Return of the Arabs: al-Qa’ida’s current military role in the Afghan insurgency’, Combating Terrorism Center at West Point 1/3 (2008), 22–25.

²³ Victor Asal and David Malet, ‘Which Conditions Increase the Likelihood of Foreign Fighters in Civil Wars?’, Presented at the International Studies Association Annual Meeting, Toronto, Ontario, 30 Mar. 2019.

²⁴ Byman, Road Warriors, 12.

²⁵ Craig Pyes, Josh Meyer, and William C. Rempel, ‘Bosnia seen as hospitable base and sanctuary for terrorists’, Los Angeles Times, 7 October 2001; Mendelsohn ‘Foreign Fighters – Recent Trends’; Cragin and Stipanovich, ‘Metastases’, 406.

²⁶ Bakke, ‘Help Wanted?’.

²⁷ Victor H. Asal et al., ‘The Softest of Targets: A Study on Terrorist Target Selection’, Journal of Applied Security Research 4/3 (2009), 258–78.

²⁸ Asal et al.

²⁹ Austin C. Doctor, ‘Foreign Fighters and Rebel Tactics’, Presented at the International Studies Association Annual Meeting, Toronto, Ontario, 30 Mar. 2019; Pauline Moore, ‘When do ties bind? Foreign fighters, social embeddedness, and violence against civilians’, Journal of Peace Research 56/2 (2019), 279–294.

³⁰ Doctor, ‘Foreign Fighters and Rebel Tactics’.

³¹ Michael C. Horowitz, ‘The Rise and Spread of Suicide Bombing’, Annual Review of Political Science 18/1 (2015), 69–84.

³² Bruce Hoffman and Gordon H. McCormick, ‘Terrorism, Signaling, and Suicide attack’, Studies in Conflict and Terrorism 27/4 (2004), 243–281.

³³ Horowitz, ‘The Rise and Spread of Suicide Bombing’.

³⁴ Vanessa Harmon et al., ‘Causes and Explanations of Suicide Terrorism: A Systematic Review’, Homeland Security Affairs 14/9 (2018), 1–60.

³⁵ Mia M. Bloom, ‘Palestinian Suicide Bombing: Public Support, Market Share, and Outbidding’, Political Science Quarterly 119/1 (2004), 61–88.

³⁶ Nick Ayers, ‘Ghost Martyrs in Iraq: An Assessment of the Applicability of Rationalist Models to Explain Suicide Attacks in Iraq’, Studies in Conflict and Terrorism 31/9 (2008), 856–882.

³⁷ The University of Chicago, ‘Chicago Project on Security and Terrorism: Suicide Attack Database’ (2014).

³⁸ Michael Horowitz, The Diffusion of Military Power: Causes and Consequences for International Politics (Princeton, NJ: Princeton University Press 2010).

³⁹ Bakke, ‘Help Wanted?’.

⁴⁰ Brian Fishman and Joseph Felter, Al-Qa’ida’s Foreign Fighters in Iraq: A First Look at the Sinjar Records (West Point: Combating Terrorism Center 2007).

⁴¹ Harun Maruf and Dan Joseph, Inside Al-Shabaab: The Secret History of Al-Qaeda’s Most Powerful Ally (Bloomington: Indiana University Press, 2018); Jason Warner and Ellen Chapin, Targeted Terror: The Suicide Bombers of al-Shabaab (West Point, NY: Combating Terrorism Center at West Point, 2018); David B. Edwards, Caravan of Martyrs: Sacrifice and Suicide Bombing in Afghanistan (Oakland, California: University of California Press 2017).

⁴² Byman, Road Warriors, 13.

⁴³ Rich and Conduit, ‘The Impact of Jihadist Foreign Fighters on Indigenous Secular-Nationalist Causes’.

⁴⁴ Hegghammer, ‘Should I Stay or Should I Go?’.

⁴⁵ Steve Coll, Ghost Wars: The Secret History of the CIA, Afghanistan, and Bin Laden, from the Soviet Invasion to 10 September 2001 (New York: Penguin Press 2004).

⁴⁶ David Malet, ‘Foreign Fighter Mobilization and Persistence in a Global Context’, Terrorism and Political Violence 27/3 (2015), 454–473.

⁴⁷ Brian Fishman et al., Bombers, Bank Accounts, and Bleedout: Al-Qa’ida’s Road In and Out of Iraq (West Point: Combating Terrorism Center 2008).

⁴⁸ We initially coded our foreign fighter data on top of the original release of REMVOD. Benjamin Acosta, ‘Dying for survival: Why militant organizations continue to conduct suicide attacks’, Journal of Peace Research 53/2 (2016), 180–196. Acosta has since released a more updated version that includes more organizations.

⁴⁹ In the codebook for the REVMOD dataset, Acosta notes that the end of a group was coded as ‘the date of elimination by force or an officially declared date of dissolution’.

⁵⁰ Malet, Foreign Fighters.

⁵¹ In our initial data collection effort, we had also hoped to find information on two more key variables: the timing in which foreign fighters participated in the organization and the size of the foreign fighter contingent within the organization. Unfortunately, we were unable to find enough quality data on these two variables to have sufficient confidence in the data to include it in our analysis.

⁵² For space considerations, we only offer brief descriptions of the variables here. Complete descriptions of these variables is available in the codebook on Acosta’s website: http://www.benjaminacosta.com/.

⁵³ A table of results for these analyses appears as Table A1 in the online appendix.

⁵⁴ This calculation was made using Gary King’s ‘clarify’ software. In each instance in which we simulated predicted values to calculate substantive effects, the rest of the variables had to be held at specific levels. All continuous variables were held at their means, while binary variables were set at fixed levels as follows: One thousand = 0, Ten thousand = 0, Islamist = 1, Leftist = 0, Self-Determination = 0, State sponsor = 0, Safe Haven = 1).

⁵⁵ This calculation was made using the ‘margins’ command in Stata.

⁵⁶ A table of results for this analysis appears as Table A1 in the online appendix.

⁵⁷ For excellent histories and analysis of al-Shabaab see Maruf and Joseph, Inside Al-Shabaab; Stig Jarle Hansen, Al-Shabaab in Somalia: The History and Ideology of a Militant Islamist Group (Oxford: Oxford University Press 2016); Mary Harper, Everything You Have Told Me Is True: The Many Faces of Al Shabaab (London: Hurst & Company 2019).

⁵⁸ ‘Counter-Terrorism in Somalia: Losing Hearts and Minds?’, 11 July (Brussels: International Crisis Group 2015); Hansen, Al-Shabaab in Somalia, 40.

⁵⁹ Tricia Bacon and Daisy Muibu, ‘The Domestication of Al-Shabaab’, Journal of the Middle East and Africa 10/3 (2019), 279–305.

⁶⁰ As Marchal argues ‘When the international press mentions the foreign fighters in Somalia, one should be aware that the term brings as much information as confusion’. Roland Marchal, ‘The Rise of a Jihadi Movement in a Country at War. Harakat al-Shabaab al Mujaheddin in Somalia’, Sciences Po CERI, 2011, 42.

⁶¹ Mendelsohn, ‘Foreign Fighters – Recent Trends’.

⁶² Harun Fazul, ‘The War against Islam: The Story of Fazul Harun Part 2’, Combating Terrorism Center at West Point, accessed 17 September 2018.

⁶³ Maruf and Joseph, Inside Al-Shabaab, 250.

⁶⁴ U.N. Security Council, Resolution 2060 (2012), Somalia report of the Monitoring Group on Somalia and Eritrea pursuant to Security Council resolution 2060 (2012), S/2013/413, 12 July (2013), 32.

⁶⁵ Mary Harper, Everything You Have Told Me Is True, 95.

⁶⁶ See Table A3 in the online appendix for a list of hotel attacks involving foreign fighters.

⁶⁷ U.N. Security Council, Resolution 2244 (2015), Somalia report of the Monitoring Group on Somalia and Eritrea pursuant to Security Council resolution 2244 (2015), S/2016/919, 31 October (2016), 32.

⁶⁸ Maruf and Joseph, Inside Al-Shabaab, 91.

⁶⁹ Maruf and Joseph, 90.

⁷⁰ S/2013/413, 57.

⁷¹ Maruf and Joseph, Inside Al-Shabaab, 91.

⁷² Maruf and Joseph, 90.

⁷³ Hansen, Al-Shabaab in Somalia, 53; U.N. Security Council, Resolution 2111 (2013), Somalia report of the Monitoring Group on Somalia and Eritrea pursuant to Security Council resolution 2111 (2013) Somalia, S/2014/726 (13 October 2014), 66–7; U.N. Security Council, Resolution 2385 (2017), Somalia report of the Monitoring Group on Somalia and Eritrea submitted in accordance with resolution 2385 (2017), S/2018/1002 (9 November 2018), 38–9.

⁷⁴ U.N. Security Council, Resolution 1724 (2006), Report of the Monitoring Group on Somalia pursuant to Security Council resolution 1724 (2006), S/2007/436, 18 July (2007), 16.

⁷⁵ S/2014/726, 66.

⁷⁶ S/2016/919, 32.

⁷⁷ S/2016/919, 145; S/2018/1002, 38–9.

⁷⁸ U.N. Security Council, Resolution 1676 (2006), Final report of the Monitoring Group on Somalia Pursuant to Security Council resolution 1676 (2006), S/2006/913, 22 Nov. (2006), 40.

⁷⁹ S/2007/436, 16.

⁸⁰ U.N. Security Council, Resolution 1766 (2007), Report of the Monitoring Group on Somalia pursuant to Security Council resolution 1766 (2007), S/2008/274, 24 Apr. (2008), 34.

⁸¹ U.N. Security Council, Resolution 1916 (2010), Report of the Monitoring Group on Somalia and Eritrea pursuant to Security Council resolution 1916 (2010), S/2011/433, 18 July (2011), 45.

⁸² ‘Somalia: Puntland Arrests Al Shabaab Members and Seizes Explosives’, Jiinwabi Media Network, 18 Nov. 2012; S/2013/413, 88.

⁸³ S/2013/413, 93.

⁸⁴ Maruf and Joseph, Inside Al-Shabaab, 141; Sarah Childress, ‘Somalia’s Al Shabaab to Ally With Al Qaeda’, Wall Street Journal, 2 Feb. 2010.

⁸⁵ Abdinasir Mohamed and Sarah Childress, ‘Suicide Bombing Kills Somali Ministers, Students’, Wall Street Journal, 4 Dec. 2009.

⁸⁶ Hansen, Al-Shabaab in Somalia, 93; David Shinn, ‘Al Shabaab’s Foreign Threat to Somalia’, Orbis 55/2 (2011), 203–15, 209.

⁸⁷ Mike Pflanz, ‘US Drone Strike in Somalia Killed Al-Shabaab “chief Bomb-Maker”’, The Telegraph, 29 Oct. 2013; Heidi Vogt and Abdalle Ahmed Mumin, ‘U.S. Kills Somali Militant’, Wall Street Journal, 29 Oct. 2013.

⁸⁸ S/2013/413, 93.

⁸⁹ Eric Schmitt, ‘Drone Strike in Somalia Is Said to Kill Shabab Leader’, The New York Times, 30 Dec. 2014, sec. Africa.

⁹⁰ Maruf and Joseph, Inside Al-Shabaab, 91.

⁹¹ S/2013/413, 57.

⁹² Michael Taarnby and Lars Hallundbaek, ‘Al-Shabaab: The Internationalization of Militant Islamism in Somalia and the Implications for Radicalisation Processes in Europe’, 26 Feb. (Copenhagen, Denmark: Danish Ministry of Justice 2010), 32.

⁹³ See Table A2 for a list of al-Shabaab’s suicide operations involving foreign fighters.

⁹⁴ S/2013/413, 68.

⁹⁵ Warner and Chapin, Targeted Terror.

⁹⁶ Fazul had written an autobiography the year before the Kampala attacks that contained a number of criticisms of al-Shabaab and strained his relationship with Godane. Fazul, ‘The War against Islam’.

⁹⁷ Patrick Mayoyo, ‘Kenyans Believed to Have Played Key Roles in Westgate Attack’, Daily Nation, 10 Aug. 2014; ‘Al-Shabaab as a Transnational Security Threat’, Mar. (Addis Ababa: Intergovernmental Authority on Development (IGAD) Security Sector Program and Sahan Foundation 2016), 37.

⁹⁸ Maruf and Joseph, Inside Al-Shabaab, 220.

⁹⁹ Maruf and Joseph, 249.

¹⁰⁰ Drazen Jorgic and Edith Honan, ‘Kenya Says It Destroys Two al Shabaab Camps in Somalia’, Reuters, 6 Apr. 2015.

¹⁰¹ U.N. Security Council, Resolution 2182 (2014), Somalia report of the Monitoring Group on Somalia and Eritrea pursuant to Security Council resolution 2182 (2014) S/2015/801, 19 Oct. (2015), 191; Edith Honan, ‘Somali Militants Vow to Turn Kenyan Cities ‘Red with Blood’, The Sydney Morning Herald, 4 Apr. 2015.

¹⁰² Humphrey Malalo, ‘Kenyan Court Convicts Three for Aiding Deadly Islamist Attack on University’, Reuters, 19 June 2019; ‘Kenya Arraigns in Court 17 Suspects of University Terror Attack’, Global Times, 8 Apr. 2015.

¹⁰³ Harun Maruf, ‘Troops Who Killed Garissa Raid Planner Had Sought to Capture Him’, Voice of America, 7 June 2016.

¹⁰⁴ Matt Bryden and Premdeep Bahra, ‘East Africa’s Terrorist Triple Helix: The Dusit Hotel Attack and the Historical Evolution of the Jihadi Threat’, Combating Terrorism Center at West Point 12/6 (2019), 1–11.

¹⁰⁵ Al-Shabaab as a Transnational Security Threat, 20.

¹⁰⁶ Al-Shabaab as a Transnational Security Threat, 20.

¹⁰⁷ Al-Shabaab as a Transnational Security Threat, 23; Ngala Chome, ‘Why Raids Are a Cause for Worry as Al Shabaab Changes Face’, The Standard, 23 July 2017.

¹⁰⁸ Author Interview with former United Nations Monitoring Group official, February 2018, Nairobi.

¹⁰⁹ U.N. Security Council, Resolution 1853 (2008), Report of the Monitoring Group on Somalia pursuant to Security Council resolution 1853 (2008), S/2010/91, 10 Mar. (2010), 50; Tricia Bacon, Interview with senior East African military official, May 2017.

¹¹⁰ Shinn, ‘Al Shabaab’s Foreign Threat to Somalia’, 210–11.

¹¹¹ Somalia: Al-Shabaab – It Will Be a Long War (Brussels: International Crisis Group, 26 June 2014); Tricia Bacon, ‘This Is Why Al-Shabab Won’t Be Going Away Anytime Soon’, Washington Post, 6 July 2017, sec. Monkey Cage.

¹¹² For example, the Big, Allied and Dangerous (BAAD) 2 dataset would be a good candidate for such a comparative analysis in the future. Unfortunately, because the groups contained in BAAD 2 do not completely overlap from those included in the Acosta dataset, collecting that data would have required more time and resources than were available.

Additional information

Notes on contributors

Tricia Bacon

Tricia Bacon is an Associate Professor in the School of Public Affairs at American University. Grace Ellis was a graduate student at American University’s School of Public Affairs. Daniel Milton is Director of Research at the Combating Terrorism Center at the United States Military Academy and an Associate Professor in the Department of Social Sciences.