Terrorism is among the most consequential and most contested concepts in political science, international law, and public discourse. It is a word that carries enormous power: to label an act or an actor "terrorist" is to place them outside the bounds of legitimate political violence, to justify extraordinary state responses, and to foreclose certain forms of engagement. Yet the concept resists agreed definition, has been applied inconsistently across political contexts, and is wielded as often for political effect as for analytical precision.

A rigorous examination of terrorism requires distinguishing what the word actually means from how it is strategically used, tracing the historical patterns of organized political violence, understanding what research tells us about how people become involved in terrorism and how terrorist campaigns end, and reckoning honestly with the civil liberties costs of the counterterrorism responses that terrorist attacks generate.

The Problem of Definition

Why Definition Matters

The aphorism "one man's terrorist is another man's freedom fighter" captures a genuine definitional problem. Actors categorized as terrorists by one party are often regarded as legitimate resisters by others, and the designation carries profound legal and moral consequences.

Alex Schmid and Albert Jongman's survey of academic and governmental definitions, published in Political Terrorism (1988), identified 109 distinct definitions in the literature, with substantial variation in what elements they included. Common components across many definitions include:

  • Use or threatened use of violence
  • Targeting of civilians or non-combatants
  • Political, ideological, or religious motivation
  • Intent to create fear beyond the immediate victims
  • A communicative or symbolic function — the violence is designed to send a message to a wider audience

The definitional problem is not merely academic. Legally, the terrorist designation removes certain protections and imposes severe penalties. Politically, it delegitimizes those to whom it is applied while legitimizing the state's response, including military force, mass surveillance, and detention practices that would otherwise be impermissible.

Bruce Hoffman in Inside Terrorism (1998, rev. 2006) proposed one of the most widely cited scholarly definitions: terrorism is "the deliberate creation and exploitation of fear through violence or the threat of violence in the pursuit of political change." The definition emphasizes the communicative function — terrorism is not primarily about the direct physical harm it causes but about the psychological and political effect it produces in an audience wider than the immediate victims.

The Method-Based Approach

Since the 1960s, the United Nations has attempted to develop a comprehensive international convention on terrorism and has repeatedly failed to agree on a definition, largely because of disagreement over whether national liberation movements targeting occupying forces should be included. This political impasse has led many scholars to propose focusing on the method rather than the actor: terrorism as a tactic — deliberate targeting of civilians for political purposes — is distinguishable from the cause in whose name it is employed. This approach allows the same actor to be both a legitimate political party and a user of terrorist tactics, and it separates condemnation of specific violent methods from judgment about the legitimacy of underlying political grievances.

Most contemporary academic definitions adopt some version of this approach while acknowledging that the boundary between combatant and civilian — and between terrorism and other forms of political violence such as guerrilla warfare, state repression, or genocide — is contested in particular cases.

State Terrorism

Academic definitions that focus on the targeting of civilians by non-state actors for political purposes risk excluding what many scholars argue is the most lethal form of political terror: state terrorism — the deliberate use of violence, intimidation, and fear by governments against their own populations or civilian populations abroad.

The Reign of Terror during the French Revolution (1793-1794), during which approximately 17,000 people were formally executed and 10,000 to 12,000 more died in detention, is the historical origin of the word "terrorism" itself. The Committee of Public Safety, led by Robespierre, openly defended terror as a revolutionary instrument. As Robespierre declared in 1794: "Terror is nothing else than justice, prompt, severe, inflexible."

In the twentieth century, state-sponsored mass violence — Stalin's purges, the Nazi Holocaust, Cambodia under the Khmer Rouge, the Guatemalan counterinsurgency campaigns of the 1970s and 1980s — killed orders of magnitude more people than any non-state terrorist campaign in history. The Global Terrorism Database (GTD), maintained by the National Consortium for the Study of Terrorism and Responses to Terrorism (START) at the University of Maryland, covers non-state attacks; it does not attempt to record state terror, reflecting both the methodological difficulty and the political sensitivity of that categorization.

Global Patterns: What the Data Shows

The Global Terrorism Database tracks terrorist incidents from 1970 to the present. By 2022, it contained records of over 200,000 terrorist attacks globally. Key patterns from the data:

Period Annual Average Attacks Notable Trend
1970s ~1,000 Rise of New Left and nationalist campaigns
1980s ~3,000 Anti-colonial and state-sponsored terrorism peak
1990s ~1,500 Post-Cold War decline in ideological terrorism
2001-2010 ~4,500 Post-9/11 surge; Iraq and Afghan conflicts
2014-2015 ~16,000 Peak years of ISIS-related violence
2018-2022 ~8,000-10,000 Decline from ISIS peak; Sub-Saharan Africa rise

(Source: Global Terrorism Database, University of Maryland, 2023)

Geographic concentration: The vast majority of terrorism deaths occur in a small number of countries. The Institute for Economics and Peace's Global Terrorism Index (2023) found that roughly 88 percent of all terrorism deaths in 2022 occurred in just 10 countries, with Afghanistan, Mali, Burkina Faso, Syria, Nigeria, Somalia, and Iraq accounting for the majority.

Lethality variation: Most terrorist attacks cause few casualties; a small number cause mass casualties. The 9/11 attacks alone account for more deaths than all terrorist attacks combined in most years of the GTD record.

Historical Waves of Terrorism

Origins: Revolution and Propaganda of the Deed

Modern terrorism as a self-conscious political tactic emerged from two distinct but overlapping origins. The Reign of Terror during the French Revolution (1793-1794), during which approximately 17,000 people were formally executed, was state terror — systematic violence by government — rather than the sub-state violence subsequently associated with the term.

The anarchist wave from roughly 1880 to 1920 introduced the modern pattern of non-state actors using spectacular violence for political communication. Anarchist theorists, particularly Peter Kropotkin, popularized the concept of "propaganda of the deed": a dramatic violent act would communicate the message of revolutionary possibility more effectively than any pamphlet. A series of high-profile assassinations followed: Tsar Alexander II in 1881, French President Sadi Carnot in 1894, Spanish Prime Minister Canovas del Castillo in 1897, Empress Elisabeth of Austria in 1898, King Umberto I of Italy in 1900, and US President William McKinley in 1901. The wave provoked the first international counterterrorism cooperation.

Rapoport's Four Waves

David Rapoport's influential "Four Waves of Terrorism" framework (2001) identified successive historical waves:

Wave Period Ideology Key Groups
Anarchist 1880s-1920s Anarchism Russian Narodnaya Volya
Anticolonial 1920s-1960s Nationalism IRA, Irgun, EOKA, FLN
New Left 1960s-1980s Marxism-Leninism Baader-Meinhof, Red Brigades, PLO
Religious 1980s-present Religious extremism Hamas, al-Qaeda, ISIS

Each wave had a distinctive ideology, organizational form, and geography. The anticolonial wave included the Irish Republican Army, the Jewish Irgun fighting British rule in Palestine, and the Algerian FLN fighting French colonialism — groups that successfully established states through combinations of political and violent pressure. The New Left wave of the 1960s and 1970s included Germany's Baader-Meinhof Group (Red Army Faction), Italy's Red Brigades, and America's Weather Underground. The religious wave, beginning with the 1979 Iranian Revolution and accelerating through Hamas, al-Qaeda, and ISIS, has been the most globally destructive.

All waves shared the communicative logic identified by the anarchists: violence as political communication to an audience beyond the immediate victims.

Rapoport's framework has been critiqued for imposing false periodization — waves overlap, and non-religious terrorism persisted within the religious wave — but it remains the most influential organizing framework for understanding the historical evolution of political violence. Some scholars have proposed a fifth wave focused on far-right and white nationalist terrorism, which grew significantly in North America and Europe in the 2010s and 2020s.

The Rise of the Far Right

The 2019 Christchurch mosque attacks in New Zealand, in which a white supremacist gunman killed 51 Muslim worshippers, exemplified a rising trend in far-right political violence. The perpetrator live-streamed the attack and published a manifesto designed to spread online — explicitly modeling the attack as propaganda of the deed for a digital age, designed to inspire copycat violence through social media amplification.

The FBI's 2022 annual report on domestic terrorism found that racially or ethnically motivated violent extremism was the most lethal domestic terrorism threat in the United States, overtaking Islamist extremism in terms of domestic attack frequency. Between 2015 and 2022, right-wing extremists committed more domestic terrorist attacks and killed more people in the United States than any other ideological category.

September 11 and the War on Terror

The Attacks

The September 11, 2001 attacks were a coordinated al-Qaeda operation in which 19 hijackers seized four commercial aircraft, crashing two into the World Trade Center towers in New York City, one into the Pentagon in Arlington, Virginia, and one — diverted by passenger resistance — into a field near Shanksville, Pennsylvania. The attacks killed 2,977 people from 93 countries, making them the deadliest terrorist attack in history and the most lethal foreign attack on American soil since Pearl Harbor.

The operational planning had begun years earlier under Osama bin Laden's direction from Afghanistan. The hijackers, most of them Saudi nationals, had spent time in the United States taking flight training. Total operational cost was estimated at $400,000 to $500,000. Al-Qaeda's strategic logic combined multiple objectives: punish the United States for its military presence in Saudi Arabia; provoke a massive American military response that would radicalize Muslim populations; demonstrate the vulnerability of the American homeland.

The Consequences

The consequences proved both predictable and miscalculated. The United States invaded Afghanistan in October 2001, dismantling the Taliban government. It subsequently invaded Iraq in 2003, a war with no demonstrable connection to the September 11 attacks. Domestically, the response included the creation of the Department of Homeland Security, the Patriot Act's expansion of surveillance powers, the detention facility at Guantanamo Bay, and the CIA's "enhanced interrogation program."

The Brown University Costs of War project estimated total costs of post-September 11 US military operations through 2021 at approximately $8 trillion, with over 900,000 deaths directly attributable to the wars. More than 38 million people were displaced. Osama bin Laden was killed in Abbottabad, Pakistan, in a US Special Forces operation on May 2, 2011.

"September 11 was not the beginning of global jihad, but it was the moment when a small organization's capacity to induce a superpower to catastrophically overreact was demonstrated to every aspiring extremist group in the world." — Jason Burke, Al-Qaeda: The True Story of Radical Islam (2003)

The September 11 attacks illustrate several recurring patterns in terrorism's political dynamics: the capacity of small groups to provoke responses vastly disproportionate to their own resources; the tension between security and civil liberties in democratic responses; and the risk that counterterrorism operations can generate new grievances that fuel further radicalization — precisely the strategic outcome bin Laden sought.

ISIS: The Territorial Caliphate

Al-Qaeda's model — a decentralized network conducting spectacular international attacks — was superseded in the 2010s by the Islamic State in Iraq and Syria (ISIS), which pursued an entirely different strategy: territorial control. At its peak in 2014-2015, ISIS controlled approximately 100,000 square kilometers of territory across Iraq and Syria and governed a population estimated at 8 million people, collecting taxes, running courts, and providing public services alongside extreme violence.

ISIS's territorial phase produced the highest death tolls from terrorism in the GTD record. The UN Assistance Mission for Iraq estimated that ISIS killed over 18,800 civilians in Iraq alone between January 2014 and October 2015. ISIS also orchestrated international attacks — Paris (2015), Brussels (2016), Manchester (2017) — and inspired "lone wolf" attacks in dozens of countries through an innovative online radicalization strategy that used social media more effectively than any previous terrorist organization.

The territorial caliphate was destroyed through military operations by a US-led coalition and local forces. By 2019, ISIS had lost all its territorial holdings. But the organization reverted to an insurgent model and continued attacks across the Middle East and Africa, while ISIS affiliates operated in West Africa, the Sahel, Southeast Asia, and elsewhere.

Radicalization Research

What We Know — and Don't

Radicalization research attempts to understand the pathway from ordinary civilian life to the willingness to commit or support political violence. Despite extensive research since 2001, no single reliable profile of a pre-terrorist emerges. The demographic and psychological diversity of people who have committed terrorist acts is substantial: they span educational levels, socioeconomic backgrounds, ages, and prior religious observance. Mental illness is not reliably more prevalent among terrorists than in the general population.

Farhad Moghaddam's staircase to terrorism model (2005) conceptualized radicalization as a funnel through which many people pass the lower floors — experiencing perceived injustice and relative deprivation — but only a small fraction ascend to the top floors of action readiness. Clark McCauley and Sophia Moskalenko's pyramid model similarly distinguishes the large population holding radical opinions from the much smaller population engaging in radical action, challenging the assumption that radical beliefs directly cause violent behavior.

Key Risk Factors

Research identifies several factors that increase (though do not determine) radicalization risk:

  • Experiences of personal or collective grievance, particularly humiliation
  • Social networks connecting the individual to others who have normalized political violence
  • Ideological frameworks that identify a clear enemy, define that enemy as deserving violent response, and frame violence as obligatory or redemptive
  • A crisis of identity or belonging that makes the certainty and community of an extremist movement attractive

Marc Sageman's network analysis of jihadi terrorists found that friendship and kinship networks — being recruited by a friend or family member already in a movement — were more consistently predictive of joining than ideology alone. People do not primarily join terrorist organizations because they encounter a compelling ideology in isolation; they join because someone they already trust draws them in.

Arie Krueger and Jitka Maleckova's 2003 cross-national analysis of terrorist recruitment found that poverty and lack of education were not reliable predictors of terrorism involvement. In some studies, terrorists were on average more educated and wealthier than the general population from which they were recruited. This finding challenged popular assumptions about deprivation-driven radicalization and suggested that ideological and social factors outweigh material conditions.

The Online Radicalization Question

The internet, social media, and encrypted messaging platforms have transformed radicalization dynamics in ways that remain only partially understood. ISIS's sophisticated use of social media — high-production propaganda videos, multilingual online magazines, dedicated Twitter accounts, and encrypted Telegram channels — produced documented cases of online radicalization with limited or no prior personal contact with established extremist networks.

J.M. Berger's analysis (2015) documented how ISIS used Twitter algorithms against themselves — exploiting the platform's recommendation systems to connect potential recruits with extremist content. The same dynamics have been documented for far-right radicalization: Zeynep Tufekci's analysis (2018, New York Times) described how YouTube's recommendation algorithm consistently directed viewers toward progressively more extreme content, creating what she called a "rabbit hole" of escalating radicalization.

However, researchers caution against overestimating online radicalization as a stand-alone pathway. Most cases involve both online and offline social connections; the internet accelerates and amplifies existing processes more than it creates entirely new ones.

The Political Critique of Radicalization Models

The radicalization concept has been criticized for overemphasizing individual psychological factors at the expense of political context. In many cases, people who committed political violence were responding to real political conditions — occupation, discrimination, state violence — that gave their actions a rationality that purely psychological models miss. The policy implication matters: if radicalization is primarily psychological, the response is therapeutic and surveillance-based; if it is primarily political, the response must address underlying grievances.

Robert Pape's analysis of suicide terrorism across 315 attacks between 1980 and 2004 (Dying to Win, 2005) found that the strongest predictor of suicide terrorism was not religious extremism but foreign military occupation. The campaigns with the highest rates of suicide attack — the Liberation Tigers of Tamil Eelam (LTTE) in Sri Lanka, Hamas in Palestine, Hezbollah in Lebanon — were organized around national liberation goals with specific, identifiable territorial demands. Religious ideology was often a secondary factor in shaping the tactic's specific form.

How Terrorist Campaigns End

The RAND Study

Seth Jones and Martin Libicki's 2008 RAND study How Terrorist Groups End analyzed the fates of 648 terrorist organizations active between 1968 and 2006:

  • 43 percent ended through policing and intelligence work
  • 40 percent ended through political processes, usually negotiation or incorporation into legitimate political structures
  • 10 percent ended through military defeat
  • 7 percent achieved their stated strategic goals

These findings are striking. Military force has a poor record as the primary counterterrorism tool, effective mainly when terrorist organizations control territory and operate in military formations. Policing and intelligence, which are labor-intensive and depend on rule-of-law frameworks and local cooperation, outperform military operations against most group types. Political accommodation — negotiating with the political movements terrorist organizations claim to represent — ends more campaigns than military defeat.

Terrorism's Strategic Effectiveness

The effectiveness of terrorism as a political strategy is contested. Terrorism rarely achieves its stated strategic goals. Bruce Hoffman argues that limited tactical successes — forcing a government to divert resources, demonstrating organizational capability, maintaining publicity — are common, but few campaigns have achieved long-term strategic objectives through violence alone.

Max Abrahms's research suggests that groups targeting civilian populations tend to be strategically less effective than groups targeting military and government targets, because civilian targeting undermines the popular support that terrorist campaigns typically need. This creates a strategic paradox: the most psychologically impactful attacks on civilians are often the most strategically counterproductive.

Nationalist and separatist campaigns have had more success than ideological or religious ones at achieving some version of their goals. The IRA's long campaign contributed to the Good Friday Agreement of 1998, though the agreement fell short of the IRA's original goal of Irish unification. The PLO's campaigns contributed to Palestinian political recognition, though not statehood. These partial successes came through eventual transition to political negotiation, not through violence achieving objectives directly.

The most comprehensive meta-analysis of terrorism's political effectiveness, conducted by Audrey Cronin in How Terrorism Ends (2009), found that terrorist campaigns end through a variety of mechanisms — decapitation of leadership (effective for some organizational types, not others), marginalizing the group by addressing legitimate grievances, negotiated settlement, and group implosion due to internal contradictions. No single factor explains all cases.

Civil Liberties and Counterterrorism

Counterterrorism policy consistently generates tension between security measures and the civil liberties protections that define constitutional governance. Specific measures impose concrete costs on individual freedoms, often falling disproportionately on minority communities.

The Post-September 11 Record

The post-September 11 United States illustrates the range of civil liberties issues at stake. The Patriot Act expanded wiretapping authority and allowed collection of business records. NSA surveillance programs revealed by Edward Snowden in 2013 showed bulk telephone metadata collection on virtually all Americans and internet surveillance programs of enormous scope. The detention of suspects at Guantanamo Bay outside normal constitutional protections, the CIA's use of "enhanced interrogation techniques" categorized by international law bodies as torture, and the targeted killing program using drones each raised fundamental rule-of-law questions.

Tomer Dragu's accountability trap model captures a structural dilemma: counterterrorism measures that reduce democratic oversight — particularly covert intelligence programs — may be more effective in the short term precisely because they are covert, but they reduce the accountability that makes democratic government legitimate.

The costs of counterterrorism since 2001 are difficult to fully quantify but well-documented in several dimensions:

  • Financial: Brown University's Costs of War Project put total US counterterrorism expenditures (military, homeland security, veterans' care, related debt interest) at over $8 trillion through 2021.
  • Human rights: The UN Special Rapporteur on Human Rights and Counter-Terrorism documented systematic violations across dozens of countries, including torture, enforced disappearances, and arbitrary detention justified under counterterrorism frameworks.
  • Civil liberties: The American Civil Liberties Union documented over 60 provisions of the PATRIOT Act that raised constitutional concerns; federal courts subsequently struck down portions of the bulk metadata collection program as unconstitutional.
  • Community impact: A 2014 Pew Research Center survey found that 81 percent of Muslim Americans were concerned about the rise of Islamic extremism, but also that 76 percent felt counterterrorism policies singled out Muslims for increased scrutiny.

The Evidence on Harsh Measures

The empirical evidence on the effectiveness of harsh counterterrorism measures is limited and often negative. Several studies find that torture produces unreliable intelligence. Mass surveillance appears less effective than targeted intelligence at identifying actual threats while generating enormous false-positive burdens on investigators. Measures perceived as discriminatory — such as indiscriminate community surveillance — can undermine the local cooperation that counterterrorism agencies depend on.

The UK's experience with internment without trial in Northern Ireland in the early 1970s is frequently cited as a case where harsh measures dramatically increased IRA recruitment and alienated the Catholic community whose cooperation was essential to effective counterterrorism. The decision to intern is now broadly considered one of the most counterproductive choices in the long history of that conflict.

Maria Rasmussen and Mohammed Hafez's (2010) review of counterterrorism strategies across multiple cases found that indiscriminate government repression consistently increased rather than decreased terrorist recruitment — the "blowback" effect. Discriminate repression targeting actual operatives while protecting civilians showed more mixed evidence. The distinction between discriminate and indiscriminate state violence turns out to be as strategically important for counterterrorism as it is morally significant.

Deradicalization Programs

Deradicalization programs attempt to move individuals who have engaged in or expressed support for political violence away from extremist beliefs. They represent a departure from purely punitive approaches and reflect research suggesting that many individuals can exit extremist movements given appropriate support and altered circumstances.

Germany's EXIT program, established in 2000, targets right-wing extremists — primarily neo-Nazis and skinhead movement members — and offers practical assistance (relocation, new identity documents, employment support) combined with psychological support. The program's founders, including former extremists turned counselors, argue that personal relationships rather than ideological argument are the primary tool: people leave extremist movements when they develop alternative relationships that provide meaning, identity, and belonging outside the movement.

Saudi Arabia's Munasaha program combines Islamic theological re-education, psychological counseling, family engagement, and vocational support. Recidivism estimates have varied widely, and independent verification of official figures is impossible.

The broader Countering Violent Extremism (CVE) policy framework developed in the United States and Europe attempts prophylactic intervention with individuals on trajectories toward radicalization. CVE programs have generated substantial controversy in Muslim communities, where they are often perceived as surveillance by another name, with community organizations pressured to report members to security services rather than support them. Research on whether CVE programs actually reduce radicalization is sparse and methodologically contested.

Tore Bjorgo's (2009) comparative analysis of exit programs across multiple countries identified consistent findings: formal ideological deradicalization is less important than practical disengagement. People leave extremist movements primarily because of changed personal circumstances — new relationships, parenthood, disillusionment with specific leaders or incidents, changed social networks. Programs that facilitate practical exit (housing, employment, documentation) show better outcomes than those focused primarily on ideological persuasion.

Frequently Asked Questions

Why is terrorism so difficult to define?

Terrorism lacks an agreed definition because the designation carries enormous political and legal consequences — delegitimizing some actors while legitimizing state responses — and because different parties apply it according to political interest. Alex Schmid (1988) found 109 distinct definitions in academic and governmental literature. The most workable approach focuses on the method (deliberate targeting of civilians for political purposes) rather than the actor, separating condemnation of specific violent tactics from judgment about underlying political grievances.

What were the historical waves of terrorism?

David Rapoport's influential framework identifies four waves: anarchist (1880s-1920s), anticolonial (1920s-1960s), New Left (1960s-1980s), and religious (1980s-present). Each wave had a distinctive ideology, organizational form, and geography, but all shared the core logic of violence as political communication to an audience beyond the immediate victims. Some scholars identify an emerging fifth wave of far-right and ethnonationalist violence.

How do terrorist campaigns typically end?

The 2008 RAND study by Jones and Libicki found that 43 percent of 648 studied organizations ended through policing and intelligence work, 40 percent through political processes, 10 percent through military defeat, and only 7 percent achieved their strategic goals. Military force is the least effective primary counterterrorism strategy; policing and political accommodation are considerably more effective.

What are the civil liberties costs of counterterrorism?

Post-September 11 counterterrorism measures in the United States included bulk surveillance of all Americans' telephone metadata (revealed by Snowden in 2013), detention at Guantanamo Bay outside constitutional protections, CIA torture, and expanded drone warfare. Evidence on harsh measures is generally negative: torture produces unreliable intelligence; indiscriminate community surveillance undermines local cooperation; and historically, internment without trial (as in Northern Ireland) has significantly increased terrorist recruitment rather than reducing it.

References

  • Schmid, A. P., & Jongman, A. J. (1988). Political Terrorism: A New Guide to Actors, Authors, Concepts, Data Bases, Theories, and Literature. Transaction Publishers.
  • Hoffman, B. (2006). Inside Terrorism (rev. ed.). Columbia University Press.
  • Rapoport, D. C. (2001). The fourth wave: September 11 in the history of terrorism. Current History, 100(650), 419-424.
  • Jones, S. G., & Libicki, M. C. (2008). How Terrorist Groups End: Lessons for Countering al Qa'ida. RAND Corporation.
  • Pape, R. A. (2005). Dying to Win: The Strategic Logic of Suicide Terrorism. Random House.
  • Burke, J. (2003). Al-Qaeda: The True Story of Radical Islam. I.B. Tauris.
  • Sageman, M. (2004). Understanding Terror Networks. University of Pennsylvania Press.
  • Moghaddam, F. M. (2005). The staircase to terrorism: A psychological exploration. American Psychologist, 60(2), 161-169.
  • McCauley, C., & Moskalenko, S. (2008). Mechanisms of political radicalization: Pathways toward terrorism. Terrorism and Political Violence, 20(3), 415-433.
  • Abrahms, M. (2006). Why terrorism does not work. International Security, 31(2), 42-78.
  • Cronin, A. K. (2009). How Terrorism Ends: Understanding the Decline and Demise of Terrorist Campaigns. Princeton University Press.
  • Krueger, A. B., & Maleckova, J. (2003). Education, poverty and terrorism. Journal of Economic Perspectives, 17(4), 119-144.
  • Bjorgo, T. (Ed.). (2005). Root Causes of Terrorism: Myths, Reality and Ways Forward. Routledge.
  • Brown University Costs of War Project. (2021). Costs of the 20-Year War on Terror: $8 Trillion and 900,000 Deaths. Watson Institute.
  • Global Terrorism Database. (2023). GTD Global Terrorism Database. National Consortium for the Study of Terrorism and Responses to Terrorism (START), University of Maryland.
  • Institute for Economics and Peace. (2023). Global Terrorism Index 2023. IEP.
  • Berger, J. M. (2015). ISIS: The State of Terror. Ecco Press.

Tags

terrorism political violence radicalization counterterrorism security political science history

Frequently Asked Questions

Why is terrorism so difficult to define and why does the definition matter?

Terrorism is among the most contested concepts in political science and international law. The aphorism 'one man's terrorist is another man's freedom fighter' captures a genuine definitional problem: actors categorized as terrorists by one party are often regarded as legitimate resisters or freedom fighters by others, and the designation carries profound legal and moral consequences. Since the 1960s, the United Nations has attempted to develop a comprehensive international convention on terrorism and has repeatedly failed to agree on a definition, largely because of disagreement over whether national liberation movements targeting occupying forces should be included.Alex Schmid and Albert Jongman's survey of academic and governmental definitions, published in Political Terrorism (1988), identified 109 distinct definitions in the literature, with substantial variation across elements. Common components across many definitions include: use or threatened use of violence; targeting of civilians or non-combatants; political, ideological, or religious motivation; intent to create fear or terror beyond the immediate victims; and a communicative or symbolic function - the violence is designed to send a message to a wider audience.The definitional problem is not merely academic. Legally, the terrorist designation removes certain protections and imposes severe penalties. Politically, it delegitimizes those to whom it is applied while legitimizing the state's response, including military force, surveillance, and detention practices that would otherwise be impermissible. When the United States designated Hamas, Hezbollah, and various Palestinian organizations as terrorist groups, it precluded legal forms of engagement with those organizations and shaped its foreign policy accordingly.Scholars have proposed focusing on the method rather than the actor to escape the political impasse: terrorism as a tactic - deliberate targeting of civilians for political purposes - is distinguishable from the cause in whose name it is employed. This approach allows the same actor to be both a legitimate political party and a user of terrorist tactics, and it separates condemnation of specific violent methods from judgment about the legitimacy of underlying political grievances. Most contemporary academic definitions adopt some version of this approach while acknowledging that the boundary between combatant and civilian, and between terrorism and other forms of political violence, is contested in particular cases.

What are the historical origins and waves of terrorism?

Modern terrorism as a self-conscious political tactic emerged from two distinct but overlapping origins: the Reign of Terror during the French Revolution, and the anarchist movement of the late nineteenth century. The French Revolutionary government used the term 'terror' approvingly to describe its systematic use of violence against perceived enemies of the Republic from 1793 to 1794, during which approximately 17,000 people were formally executed and tens of thousands more died in prisons and through revolutionary violence. This was state terror - systematic violence by government - rather than terrorism as subsequently understood as sub-state violence against governments or civilians.The anarchist wave from roughly 1880 to 1920 introduced the modern pattern of non-state actors using spectacular violence for political communication. Anarchist theorists, particularly Peter Kropotkin, popularized the concept of 'propaganda of the deed': a dramatic violent act would communicate the message of revolutionary possibility more effectively than any pamphlet, demonstrating that seemingly invulnerable rulers and institutions were vulnerable. A series of high-profile assassinations followed - Tsar Alexander II in 1881, French President Sadi Carnot in 1894, Spanish Prime Minister Canovas del Castillo in 1897, Empress Elisabeth of Austria in 1898, King Umberto I of Italy in 1900, and US President William McKinley in 1901. The wave provoked the first international counterterrorism cooperation.David Rapoport's influential 'Four Waves of Terrorism' framework (2001) identified subsequent waves: anticolonial nationalism (from the 1920s onward, including the IRA, Irgun, and EOKA), the New Left wave of the 1960s-70s (Baader-Meinhof Group, Red Brigades, Weather Underground, PLO), and the religious wave beginning in the 1980s with the Iranian Revolution, accelerating through Hamas, al-Qaeda, and reaching its most destructive expression with ISIS. Each wave had a distinctive ideology, organizational form, and geography, though all shared the communicative logic identified by the anarchists: violence as political communication to an audience beyond the immediate victims.

What happened on September 11, 2001 and what were its consequences?

The September 11, 2001 attacks were a coordinated al-Qaeda operation in which 19 hijackers seized four commercial aircraft, crashing two into the World Trade Center towers in New York, one into the Pentagon in Arlington, Virginia, and one - diverted by passenger resistance - into a field near Shanksville, Pennsylvania. The attacks killed 2,977 people from 93 countries, making them the deadliest terrorist attack in history and the most lethal foreign attack on American soil since Pearl Harbor.The operational planning had begun years earlier under Osama bin Laden's direction from Afghanistan. The hijackers, most of them Saudi nationals, had spent time in the United States taking flight training. The total operational cost has been estimated at \(400,000 to \)500,000. Al-Qaeda's strategic logic combined multiple objectives: punish the United States for its military presence in Saudi Arabia and support for Israel and Arab authoritarian governments; provoke a massive American military response that would radicalize Muslim populations and draw the United States into an unwinnable conflict; demonstrate the vulnerability of the American homeland and the organization's global reach.The consequences proved both predictable and miscalculated. The United States responded with the invasion of Afghanistan in October 2001, dismantling the Taliban government and eventually killing bin Laden in 2011. The broader response included the invasion of Iraq in 2003, the creation of the Department of Homeland Security, the Patriot Act's expansion of surveillance powers, the detention facility at Guantanamo Bay, and the CIA's enhanced interrogation program. The Brown University Costs of War project estimated total costs of post-September 11 US military operations through 2021 at approximately $8 trillion, with over 900,000 deaths directly attributable to the wars. More than 38 million people were displaced.The September 11 attacks and their aftermath illustrate several recurring patterns in terrorism's political dynamics: the capacity of small groups to provoke responses vastly disproportionate to their own resources; the tension between security and civil liberties in democratic responses to terrorism; and the risk that counterterrorism operations can generate new grievances that fuel further radicalization.

What does research tell us about how people radicalize into terrorism?

Radicalization research attempts to understand the pathway from ordinary civilian life to the willingness to commit or support political violence. Despite extensive research, no single reliable profile of a terrorist or pre-terrorist emerges from the data. The demographic and psychological diversity of people who have committed terrorist acts is substantial: they span educational levels, socioeconomic backgrounds, ages, and prior religious observance. Mental illness is not reliably more prevalent among terrorists than in the general population.Farhad Moghaddam's staircase to terrorism model (2005) conceptualized radicalization as a funnel through which many people pass the lower floors - experiencing perceived injustice and relative deprivation - but only a small fraction ascend to the top floors of action readiness and violence commitment. Clark McCauley and Sophia Moskalenko's pyramid model similarly distinguishes the large population holding radical opinions from the much smaller population engaging in radical action, challenging the assumption that radical beliefs directly cause violent behavior.Research identifies several factors that increase (though do not determine) radicalization risk: experiences of personal or collective grievance, particularly humiliation; social networks connecting the individual to others who have normalized political violence; ideological frameworks that identify a clear enemy, define that enemy as deserving violent response, and frame violence as obligatory or redemptive; and a crisis of identity or belonging that makes the certainty and community of an extremist movement attractive. Marc Sageman's network analysis of jihadi terrorists found that friendship and kinship networks - being recruited by a friend or family member - were more consistently predictive of joining than ideology alone.The radicalization concept has been criticized for overemphasizing individual pathways and psychological factors at the expense of political context. In many cases, people who committed political violence were responding to real political conditions - occupation, discrimination, state violence - that gave their actions a rationality that purely psychological models miss. The policy implication matters: if radicalization is primarily psychological, the response is therapeutic and surveillance-based; if it is primarily political, the response must address underlying grievances.

How do terrorist campaigns end and how effective is terrorism as a strategy?

Seth Jones and Martin Libicki's 2008 RAND study How Terrorist Groups End analyzed the fates of 648 terrorist organizations active between 1968 and 2006, producing findings that challenged both terrorist strategic assumptions and counterterrorism orthodoxies. The study found that 43 percent of groups ended because of successful policing and intelligence work that disrupted organizations and arrested or killed key members. Forty percent ended through political processes - usually negotiation or incorporation into legitimate political structures. Ten percent ended through military defeat. Only seven percent achieved their stated strategic goals.These findings carry several implications. First, military force has a poor record as the primary counterterrorism tool, effective mainly when terrorist organizations control territory and operate in military formations (as with some phases of ISIS). Policing and intelligence, which are labor-intensive, require local cooperation, and depend on rule of law frameworks, outperform military operations against most group types. Second, political accommodation - negotiating with terrorist organizations or the political movements they claim to represent - ends more campaigns than military defeat, suggesting that addressing political grievances can be strategically sound even when morally uncomfortable.The effectiveness of terrorism as a political strategy is contested. Terrorism rarely achieves its stated strategic goals. Bruce Hoffman argues that limited tactical successes - forcing a government to divert resources, demonstrating organizational capability, maintaining publicity - are common, but that few terrorist campaigns have achieved their long-term strategic objectives through violence alone. Max Abrahms's research suggests that groups targeting civilian populations tend to be strategically less effective than groups targeting military and government targets, because civilian targeting undermines the popular support terrorist campaigns typically need to sustain themselves.Nationalist and separatist terrorist campaigns have had more success than ideological or religious ones at achieving some version of their goals, in part because their political demands are more clearly defined and their popular constituency more identifiable. The IRA's long campaign contributed to the Good Friday Agreement of 1998, though the agreement's provisions fell far short of the IRA's original goal of Irish unification. The PLO's campaigns contributed to Palestinian political recognition, though not statehood. These partial successes came through eventual transition to political negotiation, not through violence achieving its objectives directly.

What are the civil liberties costs of counterterrorism and how should they be weighed?

Counterterrorism policy consistently generates tension between security measures and the civil liberties and human rights protections that define constitutional governance. This tension is not merely rhetorical - specific counterterrorism measures impose concrete costs on individual freedoms, often falling disproportionately on minority communities, and the cumulative effect of multiple measures can substantially alter the relationship between state and citizen.The post-September 11 United States illustrates the range of civil liberties issues at stake. The Patriot Act expanded wiretapping authority, allowed 'sneak and peek' searches without immediate notification, and permitted broad collection of business records. The NSA surveillance programs revealed by Edward Snowden in 2013 showed that the government had been collecting bulk telephone metadata on virtually all Americans and conducting internet surveillance programs of enormous scope. The detention of terrorism suspects at Guantanamo Bay outside normal constitutional protections, the CIA's use of 'enhanced interrogation techniques' that critics and international law bodies categorized as torture, and the targeted killing program using drones each raised fundamental rule of law questions about accountability, due process, and the geographic and temporal limits of the laws of war.Tomer Dragu's accountability trap model captures a structural dilemma: counterterrorism measures that reduce democratic oversight - particularly covert intelligence programs - may be more effective in the short term precisely because they are covert, but they reduce the accountability that makes democratic government legitimate. This creates a dynamic where security services can claim effectiveness for measures that cannot be publicly scrutinized or democratically evaluated.The empirical evidence on the effectiveness of harsh counterterrorism measures is limited and contested. Several studies find that torture produces unreliable intelligence, that mass surveillance is less effective than targeted intelligence, and that measures perceived as discriminatory or unjust - such as indiscriminate community surveillance - can undermine the local cooperation that counterterrorism agencies depend on. The UK's experience with internment without trial in Northern Ireland in the early 1970s is frequently cited as a case where harsh measures dramatically increased IRA recruitment and alienated the Catholic community whose cooperation was essential to effective counterterrorism.

What are deradicalization and counter-extremism programs and do they work?

Deradicalization programs attempt to move individuals who have engaged in or expressed support for political violence away from extremist beliefs and toward disengagement and, ideally, social reintegration. They represent a departure from purely punitive counterterrorism approaches and reflect research suggesting that many individuals can exit extremist movements given appropriate support, altered circumstances, and engagement with their underlying motivations.Germany's EXIT program, established in 2000, is among the most studied deradicalization initiatives. It targets right-wing extremists - primarily neo-Nazis and members of skinhead movements - and offers a combination of practical assistance (relocation, new identity documents, employment help) and psychological support to individuals who express a desire to leave extremist groups. The program's founders, including former extremists turned counselors, argue that personal relationships rather than ideological argument are the primary tool: people leave extremist movements when they develop relationships outside those movements that provide meaning, identity, and belonging on alternative terms.Saudi Arabia's Mohammed bin Nayef Counseling and Care Center (now known as the Munasaha program), established after 2003, takes a more structured approach combining Islamic theological re-education, psychological counseling, family engagement, and vocational support. Recipients receive benefits including housing and employment assistance on release. Recidivism estimates have varied widely, and critics note that Saudi official figures cannot be independently verified.The broader Countering Violent Extremism (CVE) policy framework developed in the United States and Europe after September 11 draws on deradicalization principles but applies them prophylactically, attempting to identify and intervene with individuals on trajectories toward radicalization before they commit violence. CVE programs have generated substantial controversy in Muslim communities, where they are often perceived as surveillance-by-another-name, with community organizations pressured to report members to security services rather than to support them. Research on whether CVE programs reduce radicalization is sparse and methodologically contested, partly because the programs operate in environments where the counterfactual - what would have happened without intervention - cannot be observed.

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