In a world of multiple upsetting events, from natural disasters to civil wars, terrorist attacks stand out as particularly alarming. They are surprising, brutal, and generally target the seemingly innocent. Terrorist groups rely on the shock value of these attacks to gain attention, financial backing, popular support, and new recruits from those who share their anger and thirst for change against what appear to be intransigent governments and their policies.
But when multiple terrorist groups compete for popularity, funding, and new recruits, how do their actions influence one another? This is the question Caltech professor of political science Mike Gibilisco and Casey Crisman-Cox of Texas A&M University have tried to answer.
For political scientists, the canonical case study of competing terrorist groups is the push and pull between Fatah (the secular Palestinian National Liberation Movement [PLO]) and Hamas (the Islamic Resistance Movement) as they each seek ascendance in their campaigns against Israeli policies toward Palestinian people and their lands. The competition between Fatah and Hamas is a rivalry that has been extensively documented by global watchdogs and professional researchers in the years between 1994, when the Oslo Accords between Israel and the PLO took effect, and 2018. This is the dataset upon which Gibilisco and Crisman-Cox's research rests.
Multiple explanations have been offered for why the incidence of terrorist attacks rose and fell over this period of time in the Middle East and how competition between Fatah and Hamas might have influenced that pattern. But, as Gibilisco says, "At some point we need to start quantifying which explanations best fit the data." So, in a recent paper, Gibilisco and Crisman-Cox test one possible explanation of intergroup competition that had been floated but only partially tested: outbidding.
"When applied to terrorism, outbidding-a term originally coined to describe competitive markets and their effect on prices-suggests that anti-government groups strategically use terrorist attacks to compete against one another," Gibilisco explains. "One of the more interesting aspects of the theory of outbidding is that it allows us to explain variation in terrorism independently of governmental policies and responses that these groups are trying to counter or elicit. That is, struggles between competing groups themselves may explain variation in violent attacks more than changes in external policies or provocations from governmental actors. Outbidding helps us to explain why terrorist attacks continue even when they do not seem to produce the results they are purportedly seeking."
Scholars have long hypothesized that competition between terrorist groups increases violent attacks by all groups. In outbidding, this is known as the "encouragement effect." What scholars have paid less attention to is another prediction of outbidding theory, the "discouragement effect": when individual groups decide that they cannot effectively compete with their rivals and actually decrease violent attacks.
"Imagine that you go running every weekend with a friend," Gibilisco says. "Maybe there's a healthy competition, and when you notice your friend running a little faster, you try to catch up. That's an encouragement effect. But what if your friend is a far better runner than you, and there's simply no chance that you can keep up with them? In that case you may say, 'I'll see you later,' and simply give up. Without you by their side, your friend may then run slower. That would be a discouragement effect."
Given that these effects pull in opposite directions, on the surface it would appear that the outbidding theory can account for any evidence: "If we see a positive correlation between violence and measures of competition, we can attribute that to the encouragement effect. If we see a negative correlation, that could be a discouragement effect. And if there's no apparent correlation at all, we might just say that encouragement and discouragement effects are washing each other out," Gibilisco explains. "We decided to model the outbidding theory precisely because it is difficult to figure out whether or not it is a good explanation."
Gibilisco and Crisman-Cox developed a structural approach to test the explanatory value of outbidding theory. They constructed a mathematical model of how competing groups would behave if they cared about popularity and used attacks to win that popularity. The researchers then adjusted that model to fit existing evidence about the Fatah/Hamas rivalry. After fitting the model to data, they tweaked the parameters of the model to see if the encouragement or discouragement effect arises.
Data on terrorist attacks by Fatah and Hamas were taken from the Global Terrorism Database maintained at the University of Maryland, while surveys of Palestinian opinions about Fatah and Hamas were taken from the Jerusalem Media and Communication Centre and the Palestinian Center for Policy and Survey Research, both of which survey the Palestinian population multiple times per year asking questions such as, "Which political or religious faction do you trust the most?" "Which political parties do you support?" and "If Legislative Council elections were held today, which party would you vote for?"
Once their model for outbidding was closely fit to existing data, Gibilisco and Crisman-Cox changed key parameters to see how these changes would affect the competition between Fatah and Hamas. For example, they changed the parameters of the model to see what would happen if one of the groups believed that the rival group would never use violent tactics. Would this lead them to use more or less violence? "This is like asking how fast you would run if your friend didn't show up one day," Gibilisco explains. "Would you take the opportunity to run as fast as you possibly could, to test your limits? Or would you take it easy because no one was competing with you?"
On the one hand, the researchers found evidence of the encouragement effect because their results demonstrated that the presence of Hamas encouraged Fatah to use more violence. On the other hand, Hamas was less likely to launch violent attacks during times when Fatah was significantly more popular, consistent with the discouragement effect.
Gibilisco and Crisman-Cox also asked their model to predict what would happen if one of the groups became less interested in increasing their popularity with the Palestinian people, or if the costs of mounting violent attacks rose. These manipulations also showed that both effects occurred in the rivalry: making Hamas more competitive encourages both groups to use more violence but making Fatah more competitive makes both groups use less violence.
To validate their predictions, the authors even tested their outbidding model against a model that reflects another potential explanation for patterns of violent attacks: simple, direct responses to one another's violent attacks, a tit-for-tat theory. Outbidding emerged as the more explanatory theory for the data.
Knowing that encouraging and discouraging outbidding effects are at play in competition between terrorist groups can help policymakers choose approaches that are more likely to decrease violence successfully. "Essentially, we found a surprising effect: that competition can lead to less violence owing to asymmetry between competing groups," Gibilisco explains. "Policymakers need to be sensitive to how competition and the relative popularity of different terrorist groups means that the same disincentives to terrorist violence, such as increasing the cost of attacks, may not have the desired effect on each competing group."
This research is shared in a paper titled " Tug of War: The Heterogeneous Effects of Outbidding Between Terrorist Groups " published in the Winter 2025 issue of International Organization.
