Enemies with benefits? Violent rivalry and terrorist group longevity

Abstract

Terrorist organizations often attack each other, but we know little about how this affects the involved groups. Some states encourage or turn a blind eye toward terrorist group interorganizational violence, hoping that it destroys at least one of the groups involved. This article argues that – contrary to the wishes of such governments – violent rivalries can contribute to the longevity of participating terrorist groups. Violent rivalries encourage civilians to take a side, inspire innovation, provide new incentives to group members, and spoil peace talks. Some of these mechanisms should be especially likely between rivals of different political goals (interfield rivalries), instead of between rivals seeking the same primary goal (intrafield rivalries). Illustrative cases in Colombia and Northern Ireland show that the theorized mechanisms occur in diverse environments. Quantitative global analysis of terrorist groups from 1987 to 2005, using original data on interorganizational violence, suggests that violent rivalries are generally associated with group longevity. Further analysis suggests that when rivalries are disaggregated by type, only interfield rivalries are positively associated with group longevity. Participation in violent rivalry is never found to increase a group’s chance of ending. The results suggest the importance of studying interorganizational dynamics, and raise questions about the notion of encouraging a violent rivalry as a way to hurt an involved terrorist group.

Keywords

event history analysis organizational dynamics terrorism terrorist organizations

How do violent rivalries affect terrorist groups? These relationships could harm involved terrorist organizations, leading to their destruction, yet there are also reasons to expect that rivalries could spur on groups, contributing to their endurance (e.g. Crenshaw, 1985: 483; Lichbach, 1995: 208–210, and see below). Beyond this particular puzzle, it is important to understand violent rivalries because sometimes governments turn a blind eye toward this behavior, hoping that it devastates involved groups. Government security forces have also supported one terrorist group as it attacks another, hoping to destroy the targeted organization.¹

Violent rivalries are also interesting because of broader issues relating to interorganizational dynamics of terrorist groups. Many recent analyses of terrorist groups have essentially assumed groups operate in isolation, failing to incorporate relationship attributes. The few studies to systematically explore effects of terrorist group interactions have shown important consequences, but most have focused on cooperation (Asal, Ackerman & Rethemeyer, 2012; Asal & Rethemeyer, 2008; Horowitz & Potter, 2013; Phillips, 2014). Studies of terrorist group competition have tended to look at the outcome of the level of violence more than the fate of involved groups (Bloom, 2004; Chenoweth, 2010; Findley & Young, 2012; Nemeth, 2014). Furthermore, these studies generally conceptualize ‘competition’ as political competition, and not necessarily intergroup violence. Civil war scholars conduct research on rivalry between rebel groups in the context of civil war, but this research often looks at how the war is affected, instead of consequences for groups.²

This study seeks to address these shortcomings in terrorism research by examining how violent rivalries affect group longevity. Scholars have made progress understanding why some terrorist organizations last longer than others (Jones & Libicki, 2008; Cronin, 2009; Blomberg, Gaibulloev & Sandler, 2011; Carter, 2012; Miller, 2012), but most of these studies have overlooked intergroup dynamics. I argue that having a violent rival ultimately contributes to group longevity. This occurs through four mechanisms: encouraging civilians to pick a side to support, fomenting innovation, providing additional incentives to group members, and spoiling peace talks.

The next section defines terms and presents the argument. Then I discuss several illustrative cases, to demonstrate the plausibility of the argument in contexts as diverse as Colombia and Northern Ireland. The empirical section introduces new global data on terrorist group violent rivalries, 1987–2005, and explains quantitative tests. Results suggest that having a violent rival is associated with a reduced likelihood of the group ending. Additional analysis suggests that the longevity-enhancing benefits of rivalry only occur for competitors with substantially different political goals, interfield rivals, and not for rivals from the same broader movement, intrafield rivals. The article concludes with suggestions for future research.

Terrorist groups, violent rivalries, and consequences

Terrorism is the use or threat of violence by non-state actors for the purpose of inciting fear in a much wider audience, to bring about political change (e.g. Enders & Sandler, 2012). Terrorist groups are subnational political organizations that use terrorism (Phillips, forthcoming). These groups, like other violent political groups, face what Lichbach (1995: 16) calls ‘the rebel’s dilemma’ or ‘the improbability of extensive collective dissent’. Dissident groups want sympathetic individuals to join them, but costs to the individuals can be high. These groups must stay relevant to their members, and to some degree to the public, in order to survive.

A growing body of research seeks to address the important question of terrorist group longevity. Group attributes seem to play an important role, such as the number of members (Blomberg, Gaibulloev & Sandler, 2011; Jones & Libicki, 2008), or motivations such as religion or ethnonationalism (Carter, 2012). Most studies of terrorist group tenure overlook interorganizational relationships.

Terrorist groups interact in important ways, and scholars increasingly analyze the consequences of such interactions. As noted previously, the majority of these studies look at cooperation. However, groups affect each other through other types of interaction, such as physically attacking each other or other groups’ supporters. This is violent rivalry. It is comparable to what the interstate war literature describes as rivalry, which it in turn defines as ‘militarized competition’ (e.g. Diehl & Goertz, 2000).

Interfield and intrafield violent rivalries

Between 1987 and 2005, about 15% of terrorist groups had a violent rival at some point. These relationships take a variety of forms. One distinction that can be made involves the relative goals of rivals. Some violent rivals tend to support substantially different primary goals, such as a left-wing group and a right-wing group, or groups representing competing ethnic communities. These can be referred to as interfield rivals, drawing on the notion of a ‘field’ of organizations making up a wider social movement.³ The second category of violent rivals, intrafield rivals, includes pairs of competitors that support the same primary goal, such as a communist revolution or rights for the same ethnic community. This can also be thought of as infighting (Bakke, Cunningham & Seymour, 2012: 273). Examples are the Shining Path vs. the Túpac Amaru Revolutionary Movement, and Hamas vs. Fatah.

Effects of violent rivalries

Lichbach (1995: 208–210) notes that the literature is divided on the question of whether competition between dissident groups should ultimately help or hurt them. Crenshaw (1985: 483) argues that when terrorist groups face stress from competing with each other, group members might defect or the group might splinter. Consistent with this, Staniland (2012) shows that in certain cases of ethnic conflict, intergroup ‘fratricide’ leads members to defect to join pro-state militias. Beyond internal issues, violent rivalries could lead to the destruction of one group at the hands of another. This happened in Sri Lanka in the 1980s (Bush, 2004). The potential for these outcomes is part of the reasoning behind government and popular apathy when terrorists target each other. It is also why some states have at least indirectly supported certain terrorist groups. However, my argument goes against this conventional wisdom regarding terrorist group violent rivalry.

I argue that violent rivalries should generally contribute to the endurance of involved terrorist groups, for at least four reasons. First, these relationships can help involved groups by encouraging previously unaffiliated civilians to support a group. Violent rivals could directly coerce support of civilians, or the support could come because attacks on the group inspire public sympathy. During conflicts, previously uninvolved civilians are sometimes forced to seek protection with a particular group, which can then compel them to provide support (Humphreys & Weinstein, 2006). This pattern is discussed later in case examples. It is also consistent with research showing that greater factional competition during civil wars leads to more civilian deaths (Cunningham, Bakke & Seymour, 2012). Regarding new support triggered by public sympathy, and not necessarily coerced, this is consistent with some anecdotal evidence: right-wing terrorism in Argentina in the early 1970s increased public support for the left-wing groups (Gillespie, 1995: 214), and anti-ETA terrorism in the 1980s increased sympathy for ETA (Reinares & Alonso, 2007: 125). Civilian support can be crucial for militant groups as they often rely on support networks for safe houses, information, and future recruits.

A second way that having a violent rival can help terrorist groups is that the competition can spur group learning and innovation. Organizational scholars recognize ‘the strategic importance of organizational learning as a means of providing a sustainable competitive advantage’ (Crossan, Lane & White, 1999: 522). Competition enables groups to learn new tactics as they engage each other, and it forces them to adopt new tactics if they want to survive. Terrorist groups update their behavior as new information becomes available (e.g. Enders & Sandler, 1993; Jackson et al., 2005), and they are especially likely to learn from groups with which they have a relationship. Cooperative relationships facilitate learning (Horowitz, 2010; Jackson et al., 2005), but rivals learn from each other as well. Kenney (2007) shows that ‘competitive adaptation’ occurs as illicit networks and governments interact, and such evolution is also likely between same-type actors. Direct competition between terrorist groups leads to innovations (Bloom, 2004), consistent with research on firms (Porter, 1985) and social movements (Tarrow, 1989).

Violent rivalries should also contribute to terrorist group longevity by providing new incentives for group members and potential members. Crenshaw (1985), drawing on Wilson (1973), argues that non-material incentives such as ‘purposive’ and ‘solidary’ incentives can be important for terrorist group mobilization. Purposive incentives are the sense of purpose provided to members by the organization’s political goal. However, once a group has a violent rival, a new, additional purpose appears: defend the group and its supporters from the enemy. Examples of this additional motivation – beyond the impetus of the group’s original goal, such as political change – are discussed in the case studies.

Related to this, the focus on the ‘other’ can bring together group members, deepening their bonds. These are ‘solidary incentives’, to use Wilson’s (1973) term. Krause (2013) argues that beyond tactical or strategic objectives, terrorists have organizational goals, which help explain rivalry behavior. Violent rivalries might not contribute to longer-term political goals, but they occur in the context of groups competing for popular support. The paradoxically helpful nature of interorganizational violence regarding group solidarity is comparable to Post’s (1987) argument that state repression can help reinforce the cohesiveness of terrorist groups. It is also comparable to McCauley’s notion of jujitsu politics, where counterterrorism inspires more support for the terrorist group. ‘Out-group threat produces in-group mobilization’, writes McCauley (2006: 50). Rivalries, through solidary incentives, help groups have more support than they ex ante would have due to their political goals.

The final mechanism through which violent rivalries can contribute to terrorist group longevity is in ‘spoiler’ situations (Pearlman, 2009; Stedman, 1997), by disrupting peace talks that could otherwise cause groups to give up violence. Spoiler behavior often occurs between moderates and extremists, where the latter try to undermine peace efforts (Kydd & Walter, 2002).⁴ Spoiling also happens when groups attack to prevent concessions to their enemies. Either way, the violence can cause the government to sever negotiations that could have led to voluntary group demobilization. A group in a violent rivalry might attack its rival, the state, or random civilians to spoil peace talks involving the rival. Regardless of who is attacked, spoiler behavior sometimes shuts down peace talks. As a result, terrorist groups close to giving up violence in exchange for concessions instead endure. Examples of this are discussed in the illustrative cases.

Overall, violent rivalries should contribute to terrorist group endurance though these four mechanisms: intergroup violence can encourage civilians to ‘choose a side’ and support a group, encourage crucial innovation, provide new incentives to group members, and spoil peace talks that could otherwise lead groups to give up violence. This abundance of likely benefits should generally outweigh the negative consequences of being involved in intergroup violence, such as resources used or casualties. This suggests the following general hypothesis:

Hypothesis 1: A terrorist group is less likely to end if it is involved in a violent rivalry with another terrorist group.

Interfield rivalries and group endurance

Beyond the general relationship asserted in the first hypothesis, it is possible that only certain types of violent rivalries are associated with group endurance. Two of the above mechanisms seem especially likely to apply to interfield violent rivalries. First, when violence directed at civilians forces them to pick a group to support, this situation is more likely to occur when the groups draw on different population bases for their membership – an interfield rivalry. If both competing groups are claiming to represent the same community, such as an ethnic group, they cannot indiscriminately attack members of their own community without damaging their support base. Groups in this situation, an intrafield rivalry, are more likely to directly attack each other, killing each other’s membership, and perhaps hastening the end of some groups. This was the aforementioned Sri Lanka situation. Furthermore, because of knowledge gained through interpersonal networks, groups of the same field can be threatened more by each other than by the state (Lyall, 2010).

Related to the mechanism of civilians caught between groups is the mechanism of solidary incentives. Indiscriminate attacks of a violent rival can strengthen the cohesiveness of the group. This dynamic seems straightforward with groups ideologically opposed to each other, on opposite ends of the political spectrum. With intrafield disputes, where the difference between groups is one of degree, it is not as clear that the group will strengthen and gain motivation when battling a group that ultimately wants a fairly similar political outcome. Indeed, there is evidence of intrafield rivals trying (somewhat unsuccessfully) to keep their interorganizational violence to a minimum, realizing its counterproductivity to political goals, and to each group (Morrison, 2013: 160). Overall, intrafield rivalries might not provide two of the four theorized causal mechanisms. Furthermore, they are more likely than interfield rivalries to have detrimental consequences. As a result, interfield violent rivalries should be the type of rivalry more robustly associated with group longevity.

Hypothesis 2: A terrorist group is less likely to end if it is in a violent rivalry with a group with opposite political goals, an interfield rivalry.

Illustrative cases

This section briefly discusses illustrative cases to demonstrate the plausibility of the mechanisms outlined above. Cases are considered in two geographical areas: Colombia and Northern Ireland. The unit of analysis is the individual terrorist group, but because interorganizational ties are explored, I analyze multiple groups in each area. Colombia and Northern Ireland are interesting because of the relative diversity in terrorist groups, and their relationships: violent rivalries in Colombia have been between leftist and pro-status quo groups (interfield), and also among leftist groups (intrafield). In Northern Ireland, violence has been more ethnonationalist in nature, with republican groups claiming to represent the Catholic community fighting against unionist/loyalist groups claiming to represent the Protestant community (interfield), and also in-fighting in each community (intrafield).⁵

The FARC and AUC in Colombia

The FARC has existed for decades, and attacks from so-called self-defense groups starting in the 1980s did little to weaken the FARC. On the contrary, both the FARC and the self-defense groups seemed to thrive on the competition for years. Other groups in Colombia, such as the National Liberation Army (ELN), similarly seem to have drawn inspiration and certain benefits from rivalries as well.

The FARC emerged during the violence of the mid-20th century, but a number of dynamics changed in the 1980s. During that decade, coca cultivation increased in Colombia, and the FARC imposed ‘taxes’ on coca producers. Drug traffickers, ranchers, and others started so-called self-defense groups to combat the growing leftist groups. They attacked the FARC, and also assassinated leftist politicians, union leaders, and peasants who seemed to support them. A FARC leader suggested retaliation would be strong, and that the attacks would only bring more public sympathy to the FARC (Dudley, 2004: 94).

Indeed, the paramilitary attacks inspired some peasants to support or join the FARC (Leech, 2011: 49). In 1987 the FARC increased its attacks against the self-defense groups. This in turn inspired these groups to hire Israeli mercenaries to train them in new techniques, including C-4 letter bombs, taking over houses, and shooting from moving vehicles (Dudley, 2004: 122–123). Consistent with the argument of this article, competition spurred innovation. Repeatedly throughout the 1990s, one group would attack and then ‘the tables were turned’, with the victim starting an offensive. The violence between the FARC and self-defense groups, including the United Self-Defense Forces of Colombia (AUC), continued into the 2000s, with neither group substantially weaker as a result.

The FARC has also fought other leftist groups in intrafield rivalries. In the 1990s, its animosity with the National Liberation Army (ELN) escalated. In 2000, the ELN accused the FARC of executing five of its leaders (Rochlin, 2003: 124). The groups still fight over control of drug trade and other income sources. The FARC bombed pipelines in the early 2000s largely to send a message to the ELN, which was extorting millions of dollars from oil-related interests (Wilson, 2003). The FARC in its early years focused on the government, but in recent decades its audience has widened to self-defense groups, the ELN, and others. These new enemies, and the new mission they provide for involved groups, are consistent with the notion of violent rivalries providing additional goals for the group. With new goals come additional sources of ‘sense of purpose’ for members, or in other words additional purposive incentives.

Violent rivalries also affected paramilitary groups such as the AUC. The AUC was founded in 1997 after a merger of smaller groups. It formed to fight extant leftist groups, so it always had violent rivals. Contrary to the notion of a ‘self-defense group’ simply being defensive or defeating another group to bring peace – and consistent with my argument about violent rivalries spurring on involved groups – human rights violations by all actors substantially increased in the years after the creation of the AUC (Isacson, 2008).

The AUC benefited from the continued violence of the leftist groups such as the FARC. For example, one cattle rancher who was driven off his land by the FARC, and able to return after AUC actions, said: ‘Without [the AUC], the guerrillas would be back within two hours. They are heroes here, people of glory. I will help them in any way I can’ (Wilson, 2001).

This illustrates the mechanism of civilians caught between the groups, willing to support a perceived protector. The violence of other groups also encouraged people to join the AUC. According to one survey of demobilized AUC members, half of respondents said they had joined because they felt threatened or a family member had been killed in the conflict (Villegas, 2005: 31–33).

The AUC greatly affected its rivals as well. For example, the ELN appears to have been more motivated to attack the AUC than its traditional target, the state. ‘The ELN’s most venomous attacks,’ according to Rochlin (2003: 124), ‘have been launched against its archenemy, the right-wing paramilitaries – the Autodefensas Unidas de Colombia (AUC).’

The AUC spoiled peace talks between the government and the ELN, and this seems to have directly contributed to the ELN enduring through that period. The Colombian government was poised to make considerable concessions to the ELN in 2000, but the AUC – ELN’S bitter rival – organized roadblocks across the country to protest concessions. The government backed down and negotiations collapsed (Rochlin, 2003: 125). A similar situation occurred in 2001. Romero (2003: 24) describes the AUC as a ‘definite factor’ in the failure of ELN-government negotiations. The ELN survives today, and serves as an example of violent rivalry contributing to group longevity through spoiling peace talks.⁶

The IRA and UDA in Northern Ireland

The Provisional Irish Republican Army, usually referred to as the IRA, split off of the wider nationalist movement in 1969. Since the IRA’s inception it fought with the loyalist Ulster Volunteer Force (UVF) (Bruce, 1992: 14–19; Coogan, 1995: 131), and it started fighting the loyalist Ulster Defense Association (UDA) once that group was founded in 1971. The IRA attacked bars and other public places in loyalist neighborhoods, killing unaffiliated civilians including children. The UVF and UDA responded in kind. These attacks, instead of causing members to quit or deterring new recruits, consistently inspired Catholics to join republican groups, and Protestants to join loyalist groups, in order for each type of person to protect their community or carry out revenge (e.g. Taylor, 1999: 91). This corresponds with the argument that violent rivalries can encourage previously unaffiliated citizens to join or support a terrorist group. The examples here are of interfield rivalries, which are argued to be especially likely to draw support for involved groups.

In addition to attacks carried out on third parties, the IRA also attacked members of groups such as the UVF and the UDA. During 1993, ‘for months, hardly a week passed without IRA gangs attempting to gun down or blow up those they believed to be associated with the UDA or UVF’ (McKittrick & McVea, 2000: 192). The UDA and UVF similarly attacked the IRA leadership, but such attacks were unable to destroy most of these organizations. ‘Even the best “hits” disrupt the IRA’s structure for only a few weeks before new leaders fill the vacancies’ (Bruce, 1992: 288). This suggests low odds for terrorist groups being able to actually defeat each other.

The IRA also had intrafield rivals, such as the Irish National Liberation Army (INLA) and the Irish People’s Liberation Organization (IPLO). These newer groups generally splintered off of extant groups, seeking more extreme demands (Morrison, 2013). Since these dissidents were more opposed to negotiations than the IRA, they often increased their attacks just as the IRA was talking with the British, ‘actively opposing the peace process and seeking to sabotage it’ (McKittrick & McVea, 2000: 218). The spoiler behavior theorized by Kydd & Walter (2002) has played out for decades in the form of attacks by dissident republican groups (Horgan, 2013: especially ch. 3).

While violent competition might have contributed to group longevity through spoiling peace talks among other mechanisms, there were also costs. IRA violence pressured the IPLO to disband in 1992. Various factors made the IPLO susceptible to collapse at the hands of a rival: its small membership; the group’s involvement in drug trafficking and a gang rape, which cut its public support; and infighting including the 1992 murder of a leader by dissident members (Monaghan, 2004). The IRA–IPLO rivalry was intrafield, and the fact that one group was destroyed is consistent with the second hypothesis, that this kind of rivalry does not provide the same mobilization benefits that interfield rivalries do, and can be harmful.

The UDA also benefited from rivalries. Loyalists joined the UDA as a direct reaction to IRA violence (Bruce, 1992: 216), which was at its peak in the early 1970s. Billy McQuiston, for example, witnessed the aftermath of an IRA bombing in 1971, and immediately joined the UDA. He describes leaving his swearing-in ceremony: ‘I remember when I came out, my heart was swollen with pride that I was going to do something. I was going to fight back’ (Taylor, 1999: 91). This source of motivation, consistent with purposive incentives, kept the UDA mobilized even after IRA violence started decreasing in the mid-1970s.

Once the UDA engaged in retaliatory attacks on Catholics, the back-and-forth violence became difficult to stop. Part of the spiral of violence can be explained by how people react to attacks on their community. A study of Northern Ireland residents finds that political violence victimization, or having a friend or family member victimized, makes a person more likely to support violent groups and oppose weapons decommissioning (Hayes & McAllister, 2001). This is consistent with the mechanism of violent rivalries encouraging previously uninvolved people to support a side.

Intergroup violence also inspired citizens to join groups, as militants (Taylor, 1999: 83–84). The sense of common identity between group members – solidary incentives – contributed to group loyalty and led many to oppose the peace process, out of fear of being labeled a ‘traitor’ by the community (Gallaher, 2007: 16). Some participants said their violence could defeat opposing groups. ‘I always felt the only way to beat terrorism was to terrorize the terrorist – and be better at it’, said one UDA member (Taylor, 1999: 97). This strategy seems to have backfired.

Even when the IRA was considering a ceasefire in the early 1990s, the UDA kept up its end of the violent rivalry.⁷ It used the opportunity to attack more. UDA leader Johnny Adair vocalized his reason for continuing violence, in spite of the IRA’s 1994 ceasefire: ‘These people had slaughtered our people and got away with it, and here we are, where we’re getting it right, where we’re just taking the war right to their doorstep […] scoring big time – why call a cease fire?’ (Mallie & McKittrick, 2001: 170). The desire for revenge translated into spoiling peace negotiations. Ceasefires, some of which could otherwise have resulted in groups disarming, were frequently delayed or disrupted as a result of rivalry violence.⁸

The UDA also battled newer republican groups such as the INLA and the IPLO, as well as other loyalist groups in intrafield rivalries, such as the UVF in the early 1970s (Coogan, 1995: 56) and multiple groups in the late 1990s and early 2000s (Gallaher, 2007: 13; McKittrick & McVea, 2000: 228–229). These violent rivalries gave additional purpose to the UDA, consistent with the purposive incentive argument.

Overall, the cases illustrate that violent rivalries counter-intuitively helped involved groups to survive, in the diverse situations of Colombia and Northern Ireland. The theorized mechanisms appear for organizations in interfield rivalries (FARC and AUC, IRA and UDA) as well as those in intrafield rivalries (FARC and ELN, UDA and UVF). However, as the second hypothesis suggested, interfield violent rivalries seemed to provide more of the theorized mobilization benefits.

Research design and findings

The hypotheses are tested using a global dataset of terrorist groups in existence at any point between 1987 and 2005. The primary model includes 588 terrorist groups. The unit of analysis is the group-year, and the number of observations in the primary model is 3,862. As often happens with duration analysis, many groups are not analyzed for all of their lifespan. For example, a group formed in 1980 is not analyzed until 1987, so this is considered a left-censored group. In total, 197 groups are left censored, and 229 groups are right censored, or survive past 2005.⁹ The data are an extension, with some changes, of Asal & Rethemeyer’s (2008) collection of terrorist group network data from their study of organizational lethality. The data used in that study contain information on terrorist groups that existed at some point during 1998 and 2005.¹⁰ I expanded the Asal and Rethemeyer dataset to include observations as far back as 1987, using many sources described below.

Variables in Asal and Rethemeyer’s data do not vary over time. To make the data more amenable to duration analysis, I temporally expanded the data. Their data begin in 1998, so I went back about ten years and gathered data on terrorist groups between 1987 and 1989. This essentially makes a late-1980s time wave to be compared with Asal and Rethemeyer’s late-1990s and early-2000s wave.¹¹ Examining some data in time periods is reasonable because finding yearly data for many attributes is unlikely, due to the clandestine nature of terrorism. I assume, for the purpose of these models, that terrorist group attributes in the late 1980s remain constant through the early- and mid-1990s, until the next data wave begins. This offers an advantage over data on terrorist groups that assume group attributes do not ever change (e.g. Blomberg, Engel & Sawyer, 2010; Cronin, 2009; Jones & Libicki, 2008).

The terrorist group data come from two time waves, as discussed, but because groups begin and end in specific years, the dataset is structured as group-year. Most group attributes can only vary once because they are only recorded for the two time periods. However, there is yearly variation in the relationship measures when groups form or end, and therefore enter or leave the data. For example, if two groups are violent rivals in the late 1980s, but police action eliminates one of the groups in 1992, the relationship is coded as ending that year. The surviving group is coded as not in that relationship from 1993 onward.

To determine which groups existed in the late 1980s, I examined the Asal and Rethemeyer dataset, which contains the group’s ‘age’, to determine which groups were extant as early as 1987. I also checked other group databases, primarily the Terrorist Organization Profiles (TOPs) and the Global Terrorism Database (GTD).¹² I also consulted Jones & Libicki’s data (2008).¹³

Variables and estimator

The dependent variable is Group end. It is coded 1 in the year that the terrorist group ended, if it ended during the sample. A terrorist group has ‘ended’ when it has either ceased to exist as an organization or given up terrorism as a tactic even if it remains a political group (Cronin, 2009: 210). The first scenario describes the Japanese Red Army in 2001, which disbanded after police arrested most of its members. An example of the second scenario is the IRA, which finally gave up terrorism in 2005.¹⁴ Following Cronin and others, my primary source for terrorist group end dates is the GTD and TOPs. News sources and other terrorist group datasets (e.g. Jones & Libicki, 2008) are also used. In the absence of the above, I use the year of the final reported terrorist attack of the group in the GTD. The average group in the sample reaches an age of 10.9 years. There is considerable variation, as many groups only last a few years, and others survive for decades. A majority of the groups, 354, end at some point between 1987 and 2005.¹⁵

All terrorist group variables are based on variables from Asal & Rethemeyer (2008). For years before 1998, these variables are coded using the sources described above for other terrorist group information, including TOPs and newspaper archive searches. The online Lexis-Nexis database was searched for all articles about each group. For many groups, every article about them in Lexis-Nexis during the time period was analyzed. For more prominent groups, targeted searches or books were used. These variables are coded according to Asal and Rethemeyer’s coding scheme (Asal, Rethemeyer & Anderson, 2009), although the relationship variables are changed somewhat to reflect the concepts described in my argument.

To gather information for the relationship variables, I used the same sources as described above, including searching the Lexis-Nexis database for all news articles about each group. The data I gathered for the late 1980s were then combined with the Asal and Rethemeyer data for the 1990s and early 2000s.¹⁶

Violent rival is coded 1 if the group has a violent rival, and 0 otherwise. A terrorist group is coded for this when another terrorist group physically attacks it or its supporters, or vice versa.¹⁷ Sources are largely the same as those used for other group variables. Examples of passages used for coding are in the online appendix. An additional source for Violent rival is attacks in the GTD attack list. The searchable database classifies types of targets, and two of the target types are ‘terrorists’ and ‘violent political party’. Violent rival is dichotomous instead of a count because I expect the greatest degree of variation in group duration to be explained by the difference between not having a rival and having a rival. Additionally, relatively few terrorist groups have more than one violent rival. Violent rival varies with time because of the data collection at two time points, and because relationships begin or end within the sample when a group in the relationship is either founded or ends.

To test Hypothesis 2, the variables Violent rival, inter-field, and Violent rival, intra-field are included in some models. Interfield rivals and intrafield rivals were described earlier. Group motivations come from Asal and Rethemeyer data for 1998 and later, and were coded for earlier years with the sources discussed above for other organizational variables.

The models include theoretically justified controls. Variables measuring terrorist group attributes generally come from Asal & Rethemeyer (2008) for 1998 and later. Ally is dichotomous, indicating if the group is cooperating with another terrorist organization, such as planning for or carrying out terrorist attacks together (Karmon, 2005). Sources used are the same as for other group variables. The coding of Ally for 1998 and later relies substantially on Asal & Rethemeyer’s (2008) positive relationship measure.¹⁸ Ally should be negatively related to group end, as cooperation helps groups endure (Phillips, 2014). Ally is only correlated with Violent rival at .14 (see online appendix for correlation matrix), so multicollinearity is unlikely to be a problem.

Ethnic motivation and Religious motivation are dichotomous measures indicating groups that have goals related to ethnicity or religion, respectively. These types of goals should help more with mobilization than a group being, for example, left-wing (Carter, 2012; Hoffman, 2006: 242–243; Jones & Libicki, 2008). State sponsored indicates groups that have received material support from a state. Groups that have a state sponsor should probably be less likely to end than other groups, in spite of potential negative consequences associated with state sponsorship (Carter, 2012). To code State sponsored, I consulted research by Byman (2005) in addition to sources discussed above. Drugs is a dichotomous variable indicating involvement in the production or sale of illegal drugs. This variable comes from Asal and Rethemeyer’s data for 1998 and later. For earlier years, as with other variables, it was coded from other sources as described above. It should be negatively related to Group end, as additional income should generally help the groups fund their operations and therefore survive (Piazza, 2011).

Group size is an approximation of the number of members in a terrorist group, as larger groups should be less likely to end. This variable is coded 0 for groups with fewer than 100 members, 1 for between 100 and 999 members, 2 for between 1,000 and 9,999 members, and 3 for the few groups with 10,000 or more members. This is the best measure that is available given the scarcity of information on terrorist group size (Asal & Rethemeyer, 2008; Jones & Libicki, 2008). It is measured using the same sources as other terrorist group variables. Models also include Transnational, which is coded 1 for groups that have attacked outside of the country in which they primarily operate, or have attacked foreign targets such as embassies in their own country, according to the GTD.

Measures of state attributes (yearly) are also included, based upon the state in which a group primarily operates. Population, a natural logarithm, comes from the World Bank. The variable was obtained from the Quality of Government Dataset (Teorell et al., 2011). Terrorist groups should be able to hide better in larger populations (Blomberg, Engel & Sawyer, 2010). Capabilities measures gross domestic product per capita (GDPPC), in logged thousands of 2005 US dollars. The source is the Penn World Tables (Heston, Summers & Aten, 2009). Fearon & Laitin (2003: 80) use GDPPC as a measure of ‘a state’s overall financial, administrative, police, and military capabilities’. Unfortunately, we do not have a more specific measure of state counterterrorism capabilities across countries and time. Other measures such as military spending per capita produce results that are substantively the same (see online appendix).

Regime type is measured by Polity’s 21-point measure polity2 (Marshall, Gurr & Jaggers, 2014). Regime type should be negatively related to Group end, as more democratic countries are generally constrained in their ability to fight terror. Models also include Repression, measured with the Political Terror Scale’s Amnesty International data (Gibney et al., 2014). Independently of regime type, some studies find repression positively associated with terrorism. Repression appears likely to fuel support for terrorist groups (Walsh & Piazza, 2010). Repression ranges from 1 to 5, where 5 indicates widespread state terror.

The hypotheses are tested using a discrete-time survival model. This model is used because there are time-varying covariates in the model and the data are structured as group-year. This assumes there are discrete intervals in time, even though a terrorist group can end at any point during the year. Discrete-time models are a suitable means of analyzing such data (Box-Steffensmeier & Jones, 2004; White, 1992), and for this reason recent studies of terrorist group survival on time-varying data have used such models (Blomberg, Gaibulloev & Sandler, 2011; Carter, 2012). It is basically a logistic regression that also takes time into consideration. Cubic splines are included (Beck, Katz & Tucker, 1998). Alternate approaches, such as decade or year dummies, return similar results. Because each terrorist group is measured repeatedly (each year), the standard errors are likely not independently and identically distributed (Woolridge, 2003; Zorn, 2006). To address this ‘group effects’ problem, I robustly cluster standard errors by terrorist group (Zorn, 2006).

Findings

Table I shows results of the models explaining terrorist group failure, and its inverse, longevity. In Model 1, Violent rival is statistically significant and negatively signed, suggesting that having a violent rival is associated with a lower likelihood of the group ending in a given year. This indicates support for the first hypothesis. This support is consistent across alternate specifications in the other models, and in other robustness checks discussed below. Model 2 shows Violent rival disaggregated by interfield and intrafield rivalries. Only the measure of interfield rivalries is statistically significant. This is consistent with the second hypothesis. It also adds a substantial caveat to the results of Model 1. When disaggregated, only interfield violent rivalries are negatively associated with a lower likelihood of terrorist group termination. The lack of significance for the intrafield measure could be the result of mixed consequences: sometimes, intrafield rivalries offer various theorized benefits, but in some conditions they contribute to the demise of involved groups.

Some control variables return expected results. Ally is consistently statistically significant and negative, suggesting that this type of relationship also contributes to group endurance. Ethnic motivation is also statistically significant and negative across both models, suggesting that a terrorist group with an ethnic political motivation is less likely to end in a given year than a group without such a motivation, other factors held constant. Size is also significant and negative, suggesting groups with more members are less likely to fail. These results are consistent with the literature.

Table I.

Discrete-time logit models of terrorist group termination, 1987–2005

	Model 1 Hypothesis 1	Model 2 Hypothesis 2
Violent rival	–.577 (.269)*
Violent rival, interfield		–.859 (.408)*
Violent rival, intrafield		–.513 (.385)
Ally	–1.317 (.153)**	–1.339 (.154)**
Ethnic motivation	–.398 (.179)*	–.401 (.179)*
Religious motivation	–.335 (.220)	–.327 (.219)
State-sponsored	–.311 (.236)	–.294 (.236)
Drugs	–.489 (.287)†	–.433 (.280)
Size	–.478 (.099)**	–.493 (.104)**
Transnational	–.091 (.155)	–.107 (.156)
State factors
Population (log)	–.263 (.069)**	–.262 (.068)**
Capability	–.126 (.150)	–.143 (.152)
Regime type	.016 (.019)	.018 (.019)
Repression	–.052 (.084)	–.057 (.083)
North America	1.840 (.827)*	1.816 (.822)*
South America	2.537 (.574)**	2.547 (.570)**
Europe	2.566 (.618)**	2.541 (.611)**
Sub-Saharan Africa	1.726 (.686)*	1.688 (.684)*
Asia	1.873 (.710)**	1.843 (.706)**
BIC	2,039	2,044
N (groups)	3,862 (588)	3,862 (588)

Robust standard errors are shown in parentheses. Unit of analysis is the group-year and the dependent variable is Group end. Cubic splines are not shown. Omitted region is the Middle East. Two-tailed tests: †p < .10, *p < .05, **p < .01.

Coefficients for Religious motivation, State-sponsored, and Drugs are negatively signed, but none is consistently statistically significant. Some studies find religion to be negatively associated with group failure (Blomberg, Gaibulloev & Sandler, 2011), but others find mixed results (Carter, 2012). Hoffman (2006: 242–243) suggests that ethnonationalist goals are more likely to help with endurance. Regarding state sponsorship, Carter (2012) suggests that it has a complicated relationship with group survival, and it can help or harm terrorist groups depending on different circumstances. Drugs is marginally statistically significant in Model 1 (and more so in some robustness checks) suggesting some support for the idea that involvement in the drug business helps groups endure. This has not been explored in other studies of terrorist group longevity, so it is worthy of more research.

Of the state-level control variables, only Population and regional controls are robustly statistically significant. Population is negatively signed, suggesting terrorist groups are less likely to end in more populous countries, consistent with expectations. It is noteworthy that neither State capabilities nor Regime type is statistically significant. These non-results are consistent with some research (Blomberg, Gaibulloev & Sandler, 2011), and suggest that causal factors of organizational endurance are not the same as those for terrorism generally. Regarding regions, with the Middle East as the omitted category, coefficients on all regional measures are statistically significant and positive. A terrorist group in any other region of the world is more likely to end than a terrorist group in the Middle East. Europe has the largest coefficient in the model, suggesting groups operating in Europe are especially likely to end.

Note on endogeneity

It could be that older groups such as the FARC are more likely to have a violent rival, and these types of groups are driving the results – even if they perhaps only gained a violent rival late in their lifetime. For this reason, Table II includes two types of robustness checks. Models 3 and 4 replicate the primary models, but only code groups as having an adversary if they were ‘born’ with that relationship. Results hold. Models 4 and 5 include a smaller sample, only groups founded in 1987 or later, to see if pre-1987 dynamics are driving the results. There are some changes to results for control variables, but results for hypothesized relationships are robust in these models.

Conclusion

Few studies systematically explore consequences of terrorist group rivalries for involved organizations. This article argued that violent rivalries can contribute to the longevity of involved terrorist groups through encouraging civilians to take a side, fomenting innovation, providing new incentives to members, and spoiling peace talks. Some of these mechanisms are more likely to occur with interfield rivals. Evidence from Colombia and Northern Ireland indicates that these mechanisms occur in diverse environments. Quantitative analysis of hundreds of terrorist groups from the period 1987–2005, using new data, suggests that violent rivalries are associated with group longevity. Further analysis suggests that the longevity benefits only occur with interfield rivalries.

A limitation of the article is that while it outlined a number of mechanisms through which violent rivalries could help terrorist groups endure, it did not explore which specific causal pathway found more support. Attempting to sort out these causal mechanisms would be an important next step. Additionally, the article looked at how rivalry type (interfield or intrafield) seems to condition effects of rivalries. There are probably other factors that condition rivalry effects, such as rivalry intensity or state involvement. There are few examples of violent rivalries directly leading

Table II.

Robustness checks of Models 1 and 2

	Model 3	Model 4	Model 5	Model 6
	Adversary only coded 1 if group ‘born’ with adversary		Only groups founded in 1987 or later
Violent rival	–1.530 (.622)*		–1.328 (.578)*
Violent rival, interfield		–1.494 (.609)*		–2.167 (.862)*
Violent rival, intrafield		–1.371 (1.058)		–.695 (.738)
Ally	–1.322 (.153)**	–1.322 (.153)**	–1.587 (.254)**	–1.599 (.253)**
Ethnic motivation	–.422 (.180)*	–.431 (.179)*	–.218 (.254)	–.226 (.253)
Religious motivation	–.282 (.226)	–.285 (.227)	.017 (.300)	.006 (.302)
State-sponsored	–.401 (.236)†	–.399 (.237)†	–.033 (.660)	–.064 (.656)
Drugs	–.581 (.289)*	–.578 (.289)*	–.510 (.502)	–.556 (.510)
Size	–.493 (.101)**	–.496 (.101)**	–1.040 (.220)**	–1.067 (.219)**
Transnational	–.092 (.155)	–.091 (.155)	–.618 (.228)**	–.616 (.228)**
State factors
Population (log)	–.262 (.069)**	–.262 (.069)**	–.213 (.092)*	–.211 (.092)*
Capability	–.165 (.148)	–.169 (.148)	–.189 (.205)	–.209 (.205)
Regime type	.015 (.019)	.015 (.019)	.009 (.034)	.010 (.034)
Repression	–.065 (.084)	–.069 (.084)	–.282 (.122)*	–.283 (.122)*
North America	1.890 (.832)*	1.893 (.833)*	1.028 (1.158)	1.035 (1.159)
South America	2.544 (.581)**	2.535 (.582)**	2.050 (.791)*	2.045 (.793)*
Europe	2.608 (.623)**	2.608 (.624)**	1.976 (.856)*	1.975 (.857)*
Sub-Saharan Africa	1.704 (.690)*	1.698 (.691)*	.536 (.997)	.504 (1.001)
Asia	1.797 (.712)*	1.798 (.712)*	1.384 (.992)	1.355 (.996)
BIC	2,039	2,048	1,084	1,090
N (groups)	3,862 (588)	3,862 (588)	1,717 (391)	1,717 (391)

to groups’ destruction, but they usually occur in intrafield rivalries. Further research could attempt to determine what other factors might have hastened these groups’ end.

The results raise a number of questions about counterterrorism policy, which in turn create opportunities for further analysis. The article explains why violent competition between terrorist groups usually does not destroy them – to the disappointment of some states. Governments are often tempted to confront terrorist organizations via proxy groups, but this can lead to unintended consequences. For interfield violent rivalries in particular, the rivalry could contribute to the targeted group’s longevity. Governments should generally be concerned about terrorist group longevity, so the results suggest that states should not encourage interorganizational rivalries.¹⁹

A more complicated issue, however, is that governments are interested in additional outcomes beyond the longevity of particular terrorist groups. Governments of states involved in civil wars want the war to end, perhaps via military victory. Formal theory work shows that fragmenting rebel groups and co-opting some of them can help bring an end to a civil war (Driscoll, 2012). Other research suggests that more rebel groups complicate potential negotiations, extending the duration of conflict (Cunningham, 2006). Do violent rivalries condition the effect of multiple rebel groups on civil war outcomes? Under what conditions, if any, are states likely to benefit from non-state actor rivalries? The present study examines terrorist groups, a different sample than civil war participants, but these are substantially overlapping sets, and terrorism and civil war studies speak to each other in important ways. Overall, both theory and policy benefit from a more complete understanding of terrorist organization violent rivalries, and this article sheds light on some interesting consequences of these rivalries.

Footnotes

Replication data

The dataset, codebook, and do-file for the empirical analysis in this article, along with the online appendix, can be found at .

Acknowledgements

I thank the following people for helpful comments: Victor Asal, David B Carter, Ana Carolina Garriga, Chuck Gochman, Joy Langston, James Ron, Burcu Savun, Phil Williams, and participants at presentations. I also thank Kathleen Cunningham and the anonymous reviewers. Previous versions of the project were presented at the 2011 American Political Science Association, International Studies Association, and Midwest Political Science Association annual meetings, the 2011 Political Networks Conference, and at CIDE. I thank Ian Anderson and Elsy González Cubría for help with data collection.

Notes

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