This paper was published in Al-Mesbar’s 125th monthly book — “The Psychology of Terrorism: Individuals and Terrorist Groups.
Looking back over developments in the psychology of radicalization and terrorism, several trends emerge. First was a turn away from seeing terrorists as crazy to seeing them in a rational choice framework in which at least terrorist leaders try to maximize the effectiveness of strategies and tactics. A more recent development gives greater attention to emotions in explaining terrorist behavior. Second, and related to the first, there was initially an emphasis on individual-level explanations of terrorism, then a recognition of the power of group, and most recently increased attention to the social movement and public opinion contexts in which terrorism occurs. Third, initial efforts to understand terrorism were focused on ‘them’—the terrorists. Building now, if slowly, is attention to the action-and-reaction dynamic of the conflict between terrorists and the government they oppose. In this perspective, government reactions to terrorism are as important as terrorist attacks. Finally, the slowest and most abstract trend is the beginning of recognition that terrorism and counterterrorism are politics—forms of political conflict that can be seen in relation to guerilla war and civil war.
Terrorism is the threat or use of physical violence against civilians for political gain. One of the hallmarks of a successful state is a monopoly of violence within state boundaries. To gain and to maintain this monopoly, states use violence, including torture and death, against those who live within state boundaries—mostly unarmed civilians.
Terrorism is thus very old and intimately related to state power. But use of the word terror to refer to political violence goes back only to the French Revolution of the 1790s. The revolutionaries, threatened by resistance within France and by foreign armies at the border, undertook a reign of terror to suppress the enemy within. This first violence to be called terrorism had the power of the state behind it.
State terrorism was not only first, it has been more dangerous. Rummel (1996) estimates 170 million people killed by government in the 20th century, not including 34 million dead in battle. Most of the civilian victims were killed by their own government, or, more precisely, by the government controlling the area in which the victims were living. By comparison, killing by non-state groups is small. Rummel estimates 500,000 killed in the 20th century by terrorists, guerillas, and other non-state groups.
Even unintentional killing by government forces can be significant. In Iraq and Syria, collateral damage from Coalition air strikes has been estimated to total at least 2000 civilian noncombatant deaths between 2014 and 2017.
Despite the origin of the term terrorism in reference to state violence, and despite the greater lethality of state violence, terrorism today is usually understood to mean non-state terrorism. Non-state terrorism includes anti-state terror, vigilante terror, and protection rackets, but it is anti-state terrorism that draws most attention—violence against recognized states by groups without the power of a state. This chapter focuses on anti-state terrorism, what Laqueur called terrorism “from below,” although I will end by suggesting that this terrorism cannot be understood without recognizing the role of terrorism “from above.” 
The psychological question for the chapter is this: how do individuals and groups without the power of a state become capable of political violence that includes violence against non-combatants? Rather than trying to pursue a strict chronology of answers to this question, I will take up different kinds of answer, one at a time, to show how each idea has fared. Thus I will begin with individual-difference explanations of terrorism and end with dynamic explanations. I acknowledge from the start that this chapter depends on perspectives I have gained from the work of others, especially the work of Martha Crenshaw, Donatella della Porta, and Maxwell Taylor.
Terrorism as individual pathology
A common reaction to terrorists is the thought that there must be something wrong with them. Terrorists must be crazy, or suicidal, or psychopaths without moral feelings; only someone with something wrong with him could do the cold-blooded killing that a terrorist does.
Are they crazy?
In the 1970s this suggestion was taken very seriously, but decades of research has found little evidence that terrorists are suffering from psychopathology. This research has profited by what now amount to hundreds of interviews with terrorists. Some terrorists are captured and interviewed in prison. Some active terrorists can be found in their home neighborhoods, if the interviewer knows where to look. And some retired terrorists are willing to talk about their earlier activities, particularly if these activities were successful. Itzhak Shamir and Menachem Begin, for instance, moved from anti-Arab and anti-British terrorism to leadership of the state of Israel. Interviews with terrorists rarely find anything listed in the bible of mental disorder, the Diagnostic and Statistical Manual of the American Psychiatric Association.
More systematic research confirms the interview results. Particularly thorough were the studies of the Baader-Meinhof Group—German leftist terrorists of the 1970s. Although the terrorists had gone underground and their locations were unknown, their identities were known. Excellent German records provided a great deal of information about each individual. Pre-natal and peri-natal records, pediatric records, pre-school records, lower-school records, middle-school records, high-school records, university records (most had some university education)—all of these were combed for clues. Family, neighbors, schoolmates—all who had known an individual before the leap to terrorism—were interviewed. The results of these investigations filled four volumes but are easy to summarize. The terrorists did not show any serious psychopathology. Even the four leaders who later committed suicide in a prison protest could not be diagnosed as paranoid, psychotic, or even neurotic.
Are they psychopaths?
Some have suggested that terrorists are antisocial personalities or psychopaths. Psychopaths can be intelligent and very much in contact with reality; their problem is that they are socially and morally deficient. They are law-breakers, selfish, and deceitful; they do not feel remorse for hurting others. As some individuals cannot see color, psychopaths cannot feel empathy or affection for others. Of course most psychopaths do not become terrorists.
Explaining terrorism as the work of psychopaths brings another kind of difficulty. The 9/11 attackers were willing to give their lives in the attack, but no one has ever suggested that a psychopath’s moral blindness can take the form of self-sacrifice. In addition, psychopaths are notably impulsive and irresponsible. The mutual commitment and trust evident within each of the four groups of attackers, and in the cooperation between groups, is radically inconsistent with the psychopathic personality.
It is possible that a terrorist group might recruit a psychopath for a particular mission, if the mission requires inflicting pain or death without the distraction of sympathy for the victims, but the mission would have to be a one-person job, something that requires little or no coordination and trust. And the mission would have to offer a reasonable chance of success without suicide.
The case against pathology
Of course there are occasional lone bombers or lone gunmen who kill for political causes, and such individuals may indeed suffer from some form of psychopathology. A loner like Theodore Kaczynski, the “Unabomber”, sending out letter bombs in occasional forays from his wilderness cabin, may suffer from psychopathology. But terrorists operating in groups, especially groups that can organize attacks that are successful, are very unlikely to suffer from serious psychopathology. As early as 1981 Martha Crenshaw could state confidently that “the outstanding common characteristic of terrorists is their normality” (p.390).
Indeed terrorism would be a trivial problem if only those with some kind of psychopathology could be terrorists. Rather we have to face the fact that normal people can be terrorists, that we are ourselves capable of terrorist acts under some circumstances. This fact is already implied in recognizing that military and police forces involved in state terrorism are all too capable of killing non-combatants. Few would suggest that the broad range of soldiers and police involved in such killing must all be suffering some kind of psychopathology.
If most terrorists are psychologically normal, how are they able to do abnormal things? The answer that emerged after the search for pathology failed was—group dynamics. The power of the group can move normal individuals to abnormal behavior, even denying the evidence of their own eyes in the famous Asch experiment.
Intensive study of groups began in the 1950s and led to a theory in which attraction to the group (cohesion) comes from two kinds of interdependence. The obvious kind of interdependence arises from common goals of material interest, status, congeniality, and security. The hidden interdependence arises from the need for certainty that can only be obtained from the consensus of others. Agreement with those around us is the only source of certainty about questions of value, including questions about good and evil, and about what is worth living for, working for, and dying for.
Higher cohesion leads to increased pressures for conformity to group norms, and research has shown that intergroup competition producing a shared threat is a particularly potent source of group cohesion that leads to idealizing ingroup norms, increased respect for ingroup leaders, and increased pressure on deviates. Think for instance of U.S. reactions to the 9/11 attacks.
The power of a group over its members is multiplied when that group is isolated and cut off from other sources of influence. Thus psychologists have often pointed to religious cults and small combat groups as models of how normal individuals in isolated groups are brought to extraordinary sacrifice for the group.
Even without intergroup competition there is a force for group radicalization in the phenomenon of group extremity shift (also referred to as group polarization). Research has shown that discussion in a group of like-minded individuals tends to move the group’s average opinion further in the direction favored before discussion. The shift occurs for two reasons: most discussion goes in the group-favored direction (relevant arguments), and more status is accorded individuals who are more extreme in the group-favored direction (social comparison).
In the 1980s, explanations of terrorist behavior as psychopathology declined and explanations in terms of group dynamics began to dominate. A consensus began to emerge that most terrorists are psychologically normal individuals caught up abnormal situations of intense group dynamics. Marc Sageman’s attention to self-organizing terrorist groups in the West (“Bunch of Guys”) did much to popularize the power of the group in studies of terrorism. The implication of terrorist normality was that a personality profile of potential terrorists is unlikely.
Mechanisms of Radicalization
Drawing on case material from 1800s anti-tsarist terrorists, l970s leftist terrorists, and post-9/11 jihadist terrorists, McCauley and Moskalenko identified common mechanism of radicalization at individual, small-group, and mass levels. Many of these mechanisms have been recognized by other students of terrorism.
At the individual level, mechanisms of radicalization to violent action include personal grievance, group grievance, slippery slope, love, escape, thrill and status seeking, and loss of social connection (unfreezing). Some of these mechanisms are surprisingly apolitical. Ideological motivation for political violence is usually associated with group grievance, as when jihadist terrorists refer to interpretations of the Koran to justify violence. But there are many cases where an individual without ideology or experience of political action is moved to join a militant group by personal grievance (the government harmed me or mine), love (my brother asked my help), escape (I’m safer with a gun in my hand), thrill and status seeking (I’ve always wanted to have a gun), and seeking new connections (I was alone and they welcomed me).
At the group level, as already described in the Group Dynamics section, mechanisms of radicalization to violence include group polarization, group competition, and group isolation. As noted earlier,
At the level of mass opinion, mechanisms of radicalization include jujitsu politics, hatred, and martyrdom. Hatred is a view of the enemy as a threatening bad essence that must be expelled or destroyed. Martyrdom is a source of moral outrage against perpetrators of violence against non-violent resistance. Jujitsu politics is the same dynamic of intergroup conflict and threat recognized at the group level, but now recognized as a terrorist tactic of provocation. Terrorist attacks are often attempts to provoke a government over-reaction that will, via collateral damage, increase support for the terrorists. Jujitsu politics, which aims to use the enemy’s strength against him, is now commonly recognized by scholars of terrorism. This is the 9/11 tactic that brought U.S. forces into Muslim countries, and the tactic of 2016 attacks in Europe and the U.S. that Islamic State hopes will provoke enough discrimination against Western Muslims to bring new support for Islamic State.
There are many possible combinations and orders of these 13 mechanisms, reinforcing the idea that there is likely no profile or trajectory that can identify future terrorists. But the increased salience of suicide bombers and lone-wolf terrorists in recent years has raised anew the possibility that psychopathology may be an important contributing cause of terrorism, at least for these two types of terrorist.
There is no problem understanding the psychology of those who send out suicide bombers: they are ‘smart bombs’ for non-state groups without high tech munitions. But what about the bombers? No one has studied suicide terrorists longer than Ariel Merari, who had the advantage of working in Israel during three decades in which suicide attacks have been all too common. Merari has interviewed hundreds of Palestinian terrorists, and, in his 2010 book, Driven to Death, he raised the startling possibility that there is a psychological profile that distinguishes suicide bombers from other terrorists.
Merari compared 15 would-be suicide bombers (both failed and foiled) with 12 terrorists imprisoned for offences unrelated to suicide bombing. The control cases were similar to the suicide bombers in age, education, marital status, and time in jail. Suicide bombers more likely to achieve a diagnosis of Avoidant-Dependent Personality Disorder (ADPD), and more likely to show suicidal tendencies and depressive symptoms.
The clinical picture of an individual with both Avoidant and Dependent Personality Disorder is a person completely engulfed by the will of another person or group–unwilling and unable to assert his or her own opinion for fear of criticism or embarrassment. This appears to be an individual who is easily influenced.
But this picture does not fit easily with the interviews Merari reports with 14 regional commanders of Palestinian militant groups. These men were responsible for organizing suicide missions. They said that they would not take mentally unstable individuals or suicidal individuals who want to die for personal reasons, that the predominant motive for suicide bombers was more nationalist than religious, and that half of suicide bombers were self-initiated volunteers rather than recruited. Self-initiated volunteers are not likely to be dependent-avoidant.
From these small samples no strong conclusion is possible. On balance it seems possible that a dependent personality style may be more likely among individuals ready to take direction and a suicide vest from a militant organization. Some suicide bombers may be avoiding embarrassment or criticism in their daily lives. No doubt others are moved to action by the same individual- and group-level mechanisms of radicalization identified in the previous section: revenge, outrage, and love.
But the importance of nationalist motivation—striking back against Israeli treatment of Palestinians—is a clear indication that suicide bombers cannot be reduced to a personality problem or personal difficulties.
A recent book tries for just this kind of reductionism. Lankford’s Myth of Martyrdom argues that suicide bombers are just—suicidal. Terrorist organizations recruit damaged and depressed individuals who want to die, give them a suicide vest and a target, then promote them as martyrs. Lankford concludes that Westerners should just stop falling for this propaganda.
Unfortunately for this simple tale, there is little evidence to support it. Across countries and years from 1981 to 2012, the total of suicide bombers is about 3500. How many of these were suicidal? Lankford has enough detail to analyze suicide risk factors for only 40 bombers, who are far from a representative sample (e.g no Iraqis among the 40). Most individuals with suicide risk factors never attempt suicide, but if we suppose that all 40 were indeed suicidal, Lankford has shown that an unrepresentative one percent of suicide bombers are suicidal. This attempt to make political martyrdom go away can appeal only to those desperate to see terrorism as pathology.
Lone-wolf terrorists such as Major Nidal Malik Hasan in the U.S. (2009) and Anders Breivik in Norway (2011) are a growing challenge for Western security services. They are also a challenge for psychology. The rational choice in deciding whether to join a militant group is ‘free riding.’ If terrorism succeeds, all who share the cause will join in the value of success, so the smart choice is to let others take the risks of engaging in violence. Of course individuals become soldiers and firefighters despite the risks, but the usual explanation is that organizational rewards and punishments can outweigh the risks, or, as in studies of combat soldiers, risk taking and sacrifice can be required in order not to let buddies down.
The usual explanation cannot explain the lone-wolf terrorist, who acts without organizational or group support to plan and carry out an attack alone. What can be the psychology that moves the lone actor to violence? Two possibilities have been suggested.
McCauley & Moskalenko examined school attackers and assassins because, like lone-wolf terrorists, they perpetrate planful violence that does not aim at material gain and the great majority act alone. Despite obvious demographic differences, several points of commonality emerged: some kind of grievance; a history of mental problems, especially depression; personal crisis of disconnection and maladjustment (unfreezing), and weapons experience outside the military. It seems possible that lone-wolf terrorists may often fit this disconnected-disordered profile, and indeed studies of lone-wolf terrorists often describe individuals who are loners with some history of mental disorder. The psychological implication is that individuals with a grievance but with weak social ties and the pain of mental illness may be more likely to move to lone-wolf terrorism because they have less to lose.
In addition there are some lone-wolf terrorists with good social connections and no history of mental disorder. Case materials suggest that these individuals are moved to violent action by unusual levels of sympathy for those they see as victimized by the government they try to attack (for example, Momin Khawaja). These cases, though few, suggest a caring-compelled profile. It seems that there may be that there is a dark side to empathy: individuals who most feel the suffering of others may be impelled to violence by their emotional reactions to victims.
Evolving Issues in the Psychology of Terrorism
The preceding sections represent perspectives widely shared by scholars interested in the psychology of terrorism. In this section I consider briefly some issues in which a consensus is still evolving.
The power of emotion
As early as 1981, Martha Crenshaw was emphasizing that terrorists, at least in their choice of tactics, are rational. “Significant campaigns of terrorism depend on rational political choice. As purposeful activity, terrorism is the result of an organization’s decision that it is a politically useful means to oppose a government” (p.385). This was indeed an advance over thinking of terrorists as crazy, but it led to perhaps too much reliance on rational choice models of terrorist behavior.
Choice of tactics may be rational but choice of joining a militant group may not be. Already noted are mechanisms of radicalization that imply strong emotional experience: love, hate, personal grievance (implying anger and humiliation), group grievance (implying outrage), and escape (implying fear). Case material shows terrorists up to their elbows in adrenaline and emotion. A rational-choice perspective does not deny that these emotions exist, but denies that they are in the causal chain that leads to terrorist violence. This perspective may be too narrow. Terrorism may sometimes be more about indignation than about the logic of means and ends. Over the years, three notable students of terrorism have explicitly argued that emotions can indeed push individuals and groups to terrorist violence: Jerrold Post, Donatella della Porta, and Marc Sageman.
Roles and organizations
The idea that post-911 al-Qaeda had become a ‘franchise” became popular long before any serious analysis of how al-Qaeda is or is not like McDonalds. Beginning around 2015, however, a few scholars began to look at terrorist groups and organizations with theory and research from industrial and organizational psychology.
There is an important point to be made in this kind of research. Most studies of terrorism focus on attacks and attackers—as this chapter does–but of course there are many terrorists who do not actually commit the violent acts. Some raise money, some reconnoiter and study possible targets, some acquire weapons and munitions, and so forth. As John Horgan and Paul Gill point out, we might better ask who becomes a gunman and who becomes a bomber than to ask simply who becomes a terrorist. 
Ideas versus actions
The concept of radicalization arose in reaction to the need for security services to “get to the left of the boom,” that is, to understand the events that lead up to a terrorist attack and, if possible, use these events to predict and forestall attacks. Unfortunately the concept of radicalization is at best ambivalent about whether it is radical ideas or radical action that is the focus of attention. Discussions of radicalization often assume that there is some kind of natural progression—“conveyor belt”–from bad ideas to bad actions.
This progression turns out to be very rare. Polls show that close to ten percent of U.S. Muslims believe that suicide bombing of civilians is often or sometimes justified. Projected to approximately one million U.S. Muslims, something like 100,000 agree with this radical idea. But the number of U.S. Muslims tracked or arrested by U.S. security services is only about one thousand, indicating that only about one in a hundred with radical ideas moves to violent action.
And, as already noted, many move to join a militant group for reasons that have nothing to do with ideology: personal grievance, love, escape, and status-seeking.
If 99 percent of those with radical ideas do not act, and many move to action without radical ideas, then there is no conveyor belt from ideas to action. It appears that radicalization of ideas and actions are two separate psychological problems, just as social psychologists have long recognized that, except under special circumstances (e.g. voting booth), attitudes are not strong predictors of behavior. Relatedly, research has found that giving up terrorist violence can occur with or without giving up terrorist-supporting ideas (desistence/disengagement versus deradicalization).
Separating ideas and actions is particularly important in relation to U.S. government efforts aimed at Countering Violent Extremism (CVE), which often lead to programs targeting radical ideas. Targeting bad ideas can itself produce collateral damage, especially in Western countries that officially support freedom of thought and expression.
Governments versus terrorists: a dynamic perspective
Possibly because of the directing value of government funding, terrorism research after 9/11 began with a focus on ‘them’—the terrorists. But there is the beginning of recognition that this focus is too narrow. If terrorists count on government over-reaction to build their support (jujitsu politics), then the response to terrorist attack must become part of the psychology of terrorism. Not just government response but citizen response to attack must be understood. In Chasing Ghosts, John Mueller and Martin Stewart highlight the gap between the objective dangers of terrorism and public concerns about terrorism as registered in polling data; this gap highlights the need to understand more about public response to terrorist attack.
This action-and-reaction psychology is featured in della Porta’s social-movement theorizing of terrorism. Della Porta includes vivid accounts of the conflicts between police and protestors that produced the Red Brigade terrorists in Italy and the Baader-Meinhof terrorists in Germany. Sageman’s studies of jihadist terrorists brought him to a similar perspective: “The relationship between state and protesters is dynamic and leads to unexpected developments. An explanation of the turn to violence must take into account this dynamic conflict..” (p.130).
Taking the dynamic perspective seriously leads to a syllogistic reminder that terrorism is a form of political conflict.
- Terrorism is the warfare of the weak.
- “War is the continuation of politics by other means.”
- Therefore terrorism is politics.
Here is the prospect of connecting the psychology of terrorists to the psychologies of insurgents, rebels, and soldiers in combat.
*Clark McCauley is Professor of Psychology and Co-Director of the Solomon Asch Center for Study of Ethnopolitical Conflict at Bryn Mawr College.
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 See for instance psychiatrist Jerrold Post recognizing the power of the group in Post, J.M. (1990). Terrorist psycho-logic: Terrorist behavior as a product of psychological forces. Pp. 25-40 in W. Reich (ed.) Origins of terrorism: Psychologies, ideologies, theologies, states of mind. N.Y.: Cambridge.
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McCauley, C., & Moskalenko, S. (2017). Friction: How conflict radicalizes them and us. N.Y.: Oxford.
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Three founders of modern terrorism studies reflect on what the world has learned about political violence—and what remains unknown. Atlantic, September 11. Accessed 10 Feb 2017, https://www.theatlantic.com/international/archive/2016/09/jenkins-hoffman-crenshaw-september-11-al-qaeda/499334/
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 Children may be particularly susceptible. BBC News (2016). Boko Haram crisis: ‘Huge rise’ in child suicide bombers. 12 April. Accessed 13 February 2017, http://www.bbc.com/news/world-africa-36023444
 Lankford, A. (2013). The myth of martyrdom: What really drives suicide bombers, rampage shooters, and other self-destructive killers. NY: Palgrave Macmillan.
 McCauley, C. (2014). How many suicide terrorists are suicidal? Behavioral and Brain Sciences, 37(4), 373-374.
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 McCauley, C., Quiggin, T. & Moskalenko, S. (2016). Momin Khawaja: Mechanisms of Radicalization. Final Report to the Office of University Programs, Science and Technology Directorate, U.S. Department of Homeland Security. College Park, MD: START. https://www.start.umd.edu/pubs/START_CSTAB_2.5_MominKhawajaMechanismsofRadicalization_Aug2016.pdf
 Crenshaw 1981 op. cit.
 See especially McCauley & Moskalenko 2011 op. cit., and della Porta 2013 op. cit.
 Crenshaw, M. (1981). Op. cit especially endnotes 14 and 17.
 Post 1990 op. cit., McCauley & Moskalenko 2011 op. cit., della :Porta 2013 op. cit., Sageman 2017 op. cit. See also Matsumoto, D., Hwang, H.S., & Frank, M.G. (2012). The role of emotion in predicting violence. The FBI Law Enforcement Bulletin, January. Accessed 13 Dec at leb.fbi.gov/2012/January/the-role-of-emotion-in-predicting violence.
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 Gill P, & Horgan J. (2013). Who were the volunteers? The shifting sociological and operational profile of 1240 Provisional Irish Republican Army members. Terrorism and Political Violence, 25, 435–456. Horgan, J., Shortland, N., Abbasciano, S., & Walsh, S. (2016). Actions speak louder than words: A behavioral analysis of 183 individuals convicted for terrorist offenses in the United States from 1995 to 2012. Journal of Forensic Sciences, 61(5), 1228–1237.
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 Horgan, J. (2008). Deradicalization or disengagement? A process in need of clarity and a counterterrorism initiative in need of evaluation. Perspectives on Terrorism, 2(4). Accessed 12 Feb 2017, http://www.terrorismanalysts.com/pt/index.php/pot/article/view/32/html
 See for example WORDE programs, http://www.worde.org/about/ WORDE is a member of the Office of the Director of National Intelligence Heritage Council. For English and French examples see Sageman 2017 op. cit. Chapter 3 endnote 16.
 Patel, F. (2011). Rethinking Radicalization. New York, NY: Brennan Center for Justice at New York University School of Law. Khouri, R. G. (2015). Beware the hoax of countering violent extremism. America Al Jazeera, September 29. Accessed 13 Dec 2016 at http://america.aljazeera.com/opinions/2015/9/beware-the-hoax-of-countering-violent-extremism.html
 Mueller, J. & Stewart, M.G. (2016). Chasing ghosts: The policing of terrorism. N.Y.: Oxford.
 Della Porta 2013 op. cit.
 Sageman 2017 op. cit.
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 Moskalenko, S. (2010). Civilians into warriors: Mechanisms of mobilization in US Army recruitment and training. Dynamics of Asymmetric Conflict, 3(3), 248-268.