Insurgent Defection in Civil War: Lessons from Colombia for Combating ISIS

A US Air Force F-15E Strike Eagle aircraft flies over northern Iraq after conducting airstrikes in Syria. By US Department of Defense.

Guest post by Ben Oppenheim, Abbey Steele, Juan F. Vargas, and Michael Weintraub

The Islamic State of Iraq and Syria (ISIS), also known as DAESH, engages in brutal tactics, governs harshly and effectively in territory that it captures, and profits greatly from the sale of grey market oil. It presents itself as the rightful standard-bearer for political Islam – with an agenda of radical social transformation – and has drawn recruits from across the world. ISIS also projects an air of invincibility and poses a serious risk to stability in the region. Yet recent reports indicate that combatant defections from ISIS have risen precipitously in recent months. What explains this change? Could opposing forces entice others to defect as well? More generally, why do some combatants remain in their armed groups, while others abandon the fight or defect to rival armed groups?

We take up these questions in a recent Journal of Conflict Resolution article, part of a special issue on militias in civil war. (The special issue’s relevance for the fight against ISIS is discussed by the co-editors–Corinna Jentzsch, Livia I. Schubiger, and Stathis N. Kalyvas– here.) Our piece focuses on the ongoing Colombian insurgency and – while the dynamics of violence, counterinsurgency, and group indoctrination are different in Syria/Iraq – we think common elements underlie individual defection across wars.

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Combatants can abandon their armed group in a wide variety of ways. In our article we focus on side-switching and demobilization. We define side-switching as leaving an armed group to fight for another group that represents a different ideological or ethnic constituency, while individual demobilization consists of leaving an armed group and exiting the war with the promise of receiving benefits from the government, typically in exchange for information.

To explain combatant trajectories, our theory integrates combatants’ pre-war characteristics, armed groups’ behavior during war, and the warfare they face. We reason that ideologically motivated combatants and those driven by material gain are likely to differ in terms of their responses to armed groups’ training protocols and pressure by rival armed groups, with implications for combatant resilience or defection.

To study these questions we use a representative survey of ex-combatants in Colombia from the Fundación Ideas para la Paz, a Bogotá-based think tank. The data set is unique among ex-combatant surveys because it includes a subset of left-wing insurgents who were captured during combat. We use captured combatants as a baseline against which to compare defectors and side-switchers: because the captured did not choose to leave their armed group, we infer that they are comparable to those who remain active in the group.

Three key lessons about combatant defection emerge from the Colombian conflict:

1. “True believers,” those motivated by ideology, are dedicated and resilient, but are high-risk cases for defection if an armed group deviates from its core precepts.

  • Ideologically motivated combatants are more likely to resist attempts by the state and paramilitaries to encourage defection overall, but if an armed group betrays its core beliefs, these true believers are more likely to defect. In Colombia, we found that leftist insurgents who were forced to abuse civilian populations were far more likely to defect than those who were not.

2. “Mercenaries,” fighters motivated by economic opportunity, are more likely to defect overall. But armed groups have tools at their disposal to persuade even mercenaries to fight for ideals.

  • While some fighters are motivated by deeply-held beliefs, others are motivated by a potential payday, whether opportunities for a steady paycheck or loot. Mercenaries are easier to attract than true believers. But they are also more likely to abandon an insurgency if they get a better offer from the government or rival armed groups. Insurgent groups are aware of this risk and use indoctrination to help homogenize preferences and encourage group cohesion, also reducing their odds of abandoning the group.

3. Military pressure can lead to defections, but it can also lead to resilience.

  • The international coalition battling ISIS has faced strong pressure to dramatically crush the group. But so far, airstrikes seem to have had a limited effect. Given our findings from Colombia, this is not surprising: ideologically-motivated fighters dig in when military pressure increases. Shock-and-awe counterinsurgency tactics, therefore, are not likely to induce defection when recruits are ideologically driven: a core function of ideology, which appears to have been successful in the Colombian case, is to steel individuals to remain in the fight, even under tremendous pressure.

What does this mean for ISIS?

Our work suggests that the cohesion of ISIS will depend on the profile of their recruits, its own behavior during the war, and the competition it faces with other armed groups. Ideological commitment appears to be quite high among foreign ISIS fighters. Yet we do not know very much about local recruits. Previous work on recruitment shows that armed groups’ presence in a territory tends to attract recruits, which suggests that not all combatants are likely to be “true believers.” The relative composition of the group, we argue, will make different demands of ISIS as it strives to maintain group cohesion and will create opportunities for its rivals.

If ISIS engages in acts that are perceived by ideological recruits as inconsistent with its professed ideology, then ISIS is likely to face retention problems. For example, some defectors report serious misgivings about using violence against fellow Sunnis, particularly women and children. The brutal violence of ISIS also presents an opportunity for Muslim clerics to condemn the group and highlight its un-Islamic behavior, potentially encouraging some true believers to abandon the group, while deterring those who are considering joining.

If materially motivated recruits dominate its ranks, ISIS will have to commit more resources to training and indoctrination. As the group’s wealth grows, the pool of recruits may shift towards those interested in harnessing the monetary benefits of membership. Evidence from Colombia suggests that ideological indoctrination can go some way towards alleviating these combatants’ propensity to defect when the price is right. Because we know little about the indoctrination practices that ISIS currently uses for its fighters, it is difficult to know how it may seek to change them to reflect an increased potential for combatant defections.

The most credible attacks on ISIS’s ideological consistency are those that come from defectors themselves, and counterinsurgents have a lot to gain by offering them the opportunity to denounce former comrades. Ensuring their safety could encourage others to risk defection (a highly dangerous act across many civil wars), and their experiences may deter others from joining at all. Materially motivated combatants, on the other hand, may be more likely to surrender as the result of military pressure or a bigger pay-off. A mixed strategy between military pressure and safe havens for defectors might be the best option to wear down the cohesion of ISIS.

Ben Oppenheim is a Visiting Scholar and Senior Fellow at the Center on International Cooperation, New York University. Abbey Steele is an Assistant Professor in the Department of Political Science, University of Amsterdam. Juan F. Vargas is Principal Economist CAF-Development Bank of Latin America and Professor in the Department of Economics, Universidad del Rosario
. Michael Weintraub is an Assistant Professor in the Department of Political Science, Binghamton University (SUNY).

  1. Firstly, defections have *not* risen precipitously. Actually reading the report cited in these news reports (which have an interest in overplaying this issue) will reveal that. The report contains a list of 58 people, half who are Syrian/unknown, which of up to 30,000 (foreign fighters estimate) is a ludicrously small and unrepresentative sample. That it is so small suggests defection isn’t really an issue at all. But we can still learn a few things in the IS context.

    The report contains some ‘unknowns’, but about half of them are Syrians who defected. This validates your argument that Syrians, who as locals are more likely to join for money or prestige, are more likely to defect. The report cites only 9 Westerners who defected, which supports the idea that highly ideologically-driven Western fighters are much less likely to defect

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