After September 11, 2001, Western security officials began to ask how to prevent terrorist attacks—how to “get to the left of the boom.” Radicalization became the popular term to refer to events leading up to a terrorist attack, as individuals and groups adopt radical beliefs and feelings and move to radical action. Political radicalization thus refers to change in beliefs, feelings, and actions toward increased support for one side of a political conflict.1

Radicalization occurs to both sides in the back-and-forth of conflict. Nineteen Muslims were radicalized to attack the US on 9/11, and the US was radicalized in reaction. That reaction continues in 2020, eighteen years and trillions of dollars later, with a war on terrorism abroad and a growing security state at home.

Often mentioned in relation to radicalization is political extremism. There is no objective definition of this term, but the US Government has tried to define a somewhat narrower concept, violent extremism: violent extremists are “individuals who support or commit ideologically-motivated violence to further political goals.”2 Two issues challenge this definition. First, the definition assumes that political violence is ideologically motivated. Second, the definition targets equally those who justify (“support”) political violence and those who commit political violence. 

The same two issues arise in relation to radicalization. Because radicalization includes the adoption of radical ideas, it is easy to assume that radical action, including terrorism, is caused by radical ideas. The same assumption leads to the conclusion that fighting radicalization means fighting both radical ideas and radical action

Consider first the assumption that political violence is ideologically motivated. Political violence motivated by anger or shame is lost to this definition. Nor is it clear what counts as ideology. Case histories do not show young Muslims sitting up from their reading with the sudden conviction that the Koran orders them to Jihad. Similarly, case histories do not show Right Wing terrorists rising to attack after reading Hitler’s Mein Kampf.

Political grievances are usually simpler than ideology: “They’re doing it to us and we’re not going to let them get away with it.” One might say that this counts as ideology—that motives of outrage and revenge count as ideology. In this case, ideology looks remarkably like the “moral sentiments” of empathy, indignation, and shame that are presumed to confer fitness advantages in human social interactions.3 Reference to ideology is consistent with the hegemony of rational choice theories in social science, but case materials show that radicalization to terrorism occurs in a welter of emotions.4

Now consider the idea of targeting both radical ideas and radical actions. Conflating radical opinion with radical action ignores two results of research on terrorism: 99 percent of those with radical opinions never move to radical action, and many join a militant group without previous radical ideas.5 About 100,000 US Muslims believe that suicide attacks against civilians are often or sometimes justified in defense of Islam, but fewer than a thousand are seen as security threats.  Many join a militant group for status, power, comradeship, personal revenge, or escape from life problems—not for ideology.

Sophia Moskalenko (see her TVOL article “What is Radicalization?”) and I have represented these results in a two-pyramids model of radicalization. In the opinion pyramid, levels of radicalization range from neutral, to sympathy for terrorist goals, to justifying terrorist violence, to feeling a personal obligation to take up terrorist violence. In the action pyramid, levels range from inert to legal activism, to illegal action, to terrorism (attacking civilians). The two pyramids have different psychologies; attitude and behavior are weakly related except in special circumstances (e.g. voting booth). An important implication of the two-pyramids model is that it is a mistake to target radical ideas and radical action together; there is no need to multiply enemies a hundredfold.

A recent puzzle of radicalization is homegrown terrorists. Analysis of homegrown Jihadist terrorists has emphasized sociological factors: marginal socio-economic status, experience of discrimination against Muslims, and experience in small-scale crime and prison time.6 But discrimination is not the whole story.

If Westerners discriminate against Muslims, young Muslims feel that they are not Western—not American, or English, or French. But neither are they Algerian, or Pakistani, or Nigerian; Muslims raised in Western countries have no connection to the country their parents came from. If they humiliated alike as “Muslims,” they must be Muslims.

But the news is full of stories about Western attacks in Muslim countries. More importantly, the Internet is full of videos of Muslim victims of Western attacks, and videos of Muslim heroes defending the umma.7 Discrimination in the West thus produces identification with the umma, the umma is seen as under attack, and a few Western Muslims rise in outrage to defend the umma.

To sum up, both terrorists and their targets are radicalized in the action and reaction of conflict over time. Political radicalization, both of opinions and actions, is driven more by emotion than by rational self-interest. Here is where an evolutionary perspective is useful. It is Homo emotus, not Homo economicus, who is radicalized.8   

Read the full series “Extremism in Historical and Evolutionary Perspective”:

  1. Introduction by Anthony Lopez and Hammad Sheikh
  2. The Virtue of Extremism is its Enhancement of the Ordinary by David Barash
  3. Extremism as Defense by Rose McDermott
  4. Why Extremism Isn’t the Real Issue by Mark Sedgwick
  5. What is Radicalization? by Sophia Moskalenko
  6. Conservative Extremists Are Afraid of Threats That Don’t Exist by Colin Holbrook and Jennifer Hahn-Holbrook
  7. Extremist Violence Has Its Roots in Morality, Not Ideology by Clark McCauley
  8. In the Eye of the Beholder: Parochial Altruism, Radicalization, and Extremism by Zoey Reeve
  9. Hidden Figures: The Untold Story of Terrorist Recruiters by John Horgan and Katerina Papatheodorou
  10. Why Terrorists Are Misunderstood by Max Abrahms
  11. Why Religious Extremism is Maladaptive by Richard Sosis
  12. The Extremist in Historical Perspective: Lessons from the Era of Anarchist Terrorism by Randall Law
  13. Terrorism and the Apocalyptic by Charles B. Strozier
  14. Extremist Groups Require the Greatest Trust Among Members by Melissa McDonald
  15. Moral Rigidity Evolved to Strengthen Bonds Within Groups by Antoine Marie
  16. Sacred Values, Social Identities, and Extremist Violence by Nafees Hamid


[1] Moskalenko, S., & McCauley, C. (2017). “Understanding Political Radicalization: The Two Pyramids Model,”  American Psychologist, 72(3), 205-216.

[2] Executive Office of the President of the United States. (October 2016). Strategic Implementation Plan for Empowering Local Partners to Prevent Violent Extremism in the United States, p. 2, footnote 2.  https://www.dhs.gov/sites/default/files/publications/2016_strategic_implementation_plan_empowering_local_partners_prev.pdf

[3] Stoelhorts, J. W. (2017) “Moral Sentiments,” In D. S. Wilson, M. Van Vugt, & M. Beilby (Eds.), This View of Business: How Evolutionary Thinking Can Transform the Workplace, pp. 11-12.  https://new.evolution-institute.org/wp-content/uploads/2017/09/tvol-biz-publication-1.pdf

[4] McCauley, C., & Moskalenko, S. (2017).  Friction 2d edition: How Conflict Radicalizes Them and Us. New York: Oxford University Press.

[5] Ibid.

[6] McCauley, C. R. (2018). “Explaining Homegrown Western Jihadists: The Importance of Western Foreign Policy,” International Journal of Conflict and Violence, 12, 1-10. doi: 10.4119/UNIBI/ijcv.643 http://www.ijcv.org/index.php/ijcv/article/view/643/pdf

[7] Holt, T., Freilich, J. D., Chermak, S., & McCauley, C. (2015). “Political Radicalization on the Internet: Extremist Content, Government Control, and the Power of Victim and Jihad Videos,” Dynamics of Asymmetric Conflict, 8(2), 107-120.

[8] Stoelhorts, op cit.

Header image by The Naked Ape via Flickr

Published On: January 30, 2020

Clark McCauley

Clark McCauley

Clark McCauley is Research Professor of Psychology at Bryn Mawr College.  His research interests include stereotypes, group dynamics, and the psychological foundations of ethnic conflict and genocide.  He is co-author of Why Not Kill Them All? The Logic and Prevention of Mass Political Murder (2006), co-author of Friction: How Radicalization Happens to Them and Us (2011, second edition 2017), co-author of The Marvel of Martyrdom: The Power of Self-Sacrifice in a Selfish World (2018), and Founding Editor emeritus of the journal Dynamics of Asymmetric Conflict: Pathways toward Terrorism and Genocide.  He is a lead investigator with the National Consortium for Study of Terrorism and Responses to Terrorism (START).


  • Steve Davis says:

    The author wrote; “It is Homo emotus, not Homo economicus, who is radicalized.”

    I hope this was not an endorsement of homo economicus; after all, it was homo economicus in the blind pursuit of the economics of individualism that has been a major influence in creating the chaos and turmoil that leaves many thinking they have no alternative but to become radical.

  • Malek Al Kuffar says:

    It’s difficult to understand how someone posing as an expert can be so ignorant as to reduce Islamic extremism to a reaction against American or western aggression. Half a dozen European countries that have never sent troops abroad are likewise attacked by Islamic terrorists. Argentina too was the victim of a completely unprovoked massacre by Hezbollah in 1994. Islamic aggression is constantly carried out against Christians of Egypt and other African countries that cannot even remotely be associated with US imperialism. In Pakistan, Iraq and other countries, Muslims of different sects slaughter each other with the same ferocity as they attack Westerners.
    “Muslims raised in Western countries have no connection to the country their parents came from. If they humiliated alike as “Muslims,” they must be Muslims.” That is a phenomenon that only happens in one religion. It doesn’t happen to Hindus, Christians, Buddhists, Sikhs or atheists. Consequently if they identify as Muslims, this is an exclusively Muslim pathological phenomenon. For people fundamentally different to identify with each other solely on the basis of some religious creed means that there is something wrong with Islam. Especially since they are at each other’s throats most of the time and only join forces when there is some outsider to be combatted.
    If the the Internet is full of videos of Muslim victims of Western attacks, that’s because they do not want to show all the Muslim victims of Muslim attacks, who are much more plentiful. During the 5 years before the US invaded Afghanistan, Pakistani troops collaborated with the Taliban and Al Qaeda in conducting genocidal atrocities against whole regions of Afghanistan. Those photos are never shown on the internet because jihadi propagandists don’t find it convenient to do so.
    Blowback is largely a product of paranoid conspiracy theories generated on an industrial scale by jihadi propagandists. I’m not denying that aggression by some western countries exists. Actually only 3 or 4 western countries. Islamic terrorism is something that stems from Islamic doctrine.

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.