25 Years After the 9/11 Terrorist Attacks

INTRODUCTION

The attacks of September 11, 2001 (9/11), carried out by Al-Qaeda against multiple targets on U.S. soil, were the catalyst for a structural transformation of transnational terrorism. The U.S. response, centered on the military priority of the “war on terror,” succeeded in dismantling Al-Qaeda’s centralized threat. At the same time, however, it accelerated the decentralization of the phenomenon, giving way to more diffuse and adaptive forms of terrorism.

Twenty-five years later, jihadist terrorism no longer occupies a dominant place on the international security agenda, having been displaced by great-power competition. Nevertheless, its effects, such as the fragmentation of terrorism and securitization, remain a lasting legacy even in countries unrelated to the original conflict, such as Chile. The following sections analyzes the 9/11 attack through the lens of terrorism literature; then briefly assess the Western response; next, summarizes the current state of terrorism and, finally, raises certain implications for the case of Chile.

1. 9/11 THROUGH THE LENS OF TERRORISM LITERATURE

Given the multiplicity of definitions the academic literature offers for the concept of terrorism, the Al-Qaeda attack satisfies almost all of them, as it constituted a previously organized violent act against civilians, that had a political aim and produced an impact on an audience. The following section reviews the literature supporting each of these dimensions, beginning with the rational and planned nature of the attack. First, the rational choice model, proposed by Martha Crenshaw[i] in agreement with Mulaj[ii], Hoffman[iii], and Schmid[iv], holds that terrorism constitutes a form of political violence resulting from a rational choice whose primary victims are civilians. This implies the existence of a planning process and a weighing of costs and benefits, rather than a spontaneous action.

Such a rational choice requires a concrete strategy to be carried out. On this point, Kydd and Walter[v] argue that terrorism constitutes a form of costly signaling and that, therefore, no counterterrorism policy can be formulated or be effective without first understanding the strategic logic that underpins it. Of the five strategies they identify – attrition, intimidation, provocation, spoiling, and outbidding – 9/11 fits within the logic of provocation, as a weak actor used violence to its advantage in order to force a state overreaction capable of radicalizing the civilian population that supports its political objective.

Regarding the political objectives of terrorism, Kydd and Walter identify five categories: policy change, territorial change, regime change, social control, and maintenance of the status quo, or a combination thereof. In Al-Qaeda’s case, the predominant objective was policy change, since the attack sought to compel the United States to withdraw its troops from the Middle East and end its economic support for Israel.

Another central element of terrorism is Schmid’s notion of “armed communication,” which locates the psychological impact on a large audience above and beyond material damage[vi]. This impact is achieved by violently attacking civilians or non-combatants to instill fear under the logic of “I could be next,” generating pressure on the government to achieve the terrorists’ specific political objective. So, the effectiveness of the act depends on media amplification, and 9/11 perfectly illustrates this logic by using thousands of innocent victims as a visual backdrop to terrorize public opinion and challenge the American state.

Thus, Al-Qaeda, which planned and executed a clear strategy of provocation against the West, represented by the United States; which hijacked commercial aircraft to simultaneously attack deliberately crowded and populated symbols of capitalism, democracy, and military power; and which killed more than 3,000 people with the aim of having the United States withdraw its support for Israel and Saudi Arabia, meets the fundamental elements that the literature attributes to the phenomenon of terrorism.

Figure 1. Key Elements for Defining Terrorism (9/11)

Source: Own elaboration based on Crenshaw, Kydd and Walter, and Schmid.

2. EFFECTIVENESS OF THE RESPONSE

The response to 9/11, embodied in counterterrorism policies and military intervention, succeeded in containing the threat by reducing Al-Qaeda’s immediate operational capacity, but it failed to address the underlying causes. Through the “Global War on Terror” (GWOT), it was mistakenly assumed that destroying the organization would weaken its ideology, overlooking the underlying factors that allow terrorism to expand.

The Western military response after 9/11 revealed some of the limitations of this strategy for eradicating the long-term threat of global jihadism. While allied actions succeeded in degrading Al-Qaeda’s operational capacity and preventing attacks of similar magnitude, the strategy of capturing and eliminating leaders, known as organizational decapitation, proved insufficient. This Western tactical approach overlooked the fact that jihadism is not a conventional hierarchical structure but a bureaucratized, decentralized, and ideologically entrenched network capable of surviving the removal of its top leadership[vii].

These tactical flaws were compounded by counterproductive strategic consequences caused by the excessive use of force and the erosion of certain human rights. The Western response helped destabilize the Middle East, creating both the “permissive conditions” (the environment of instability) and the precipitating factors (direct abuses) that Crenshaw identifies as conducive to the spread of terrorism. Consistent with the strategic logic of provocation explained above, the violation of freedoms not only eroded Western legitimacy but also fed the radical narrative by exacerbating the grievances that drive recruitment.

In terms of effectiveness, the military response can also be assessed based on its cost. If the goal was to neutralize the threat of a group with comparatively marginal resources, the investment of nearly $8 trillion and the deaths of more than 900,000 people[viii] over twenty years appear disproportionate. As evidenced in the Global Terrorism Index[ix], the West did not eliminate the terrorist threat. In fact, it experienced a severe increase in attacks and deaths between 2015 and 2017 due to the proliferation of smaller-scale terrorist incidents, which demonstrates the decentralization and adaptation of the phenomenon. The disproportion between the investment and the persistence of the threat is itself evidence of low effectiveness[x].

Figure 2. Deaths from terrorism in the West, 2007–2025. Source: Institute for Economics & Peace, Global Terrorism Index 2026 (Sydney: Institute for Economics & Peace, 2026), 34, figure 2.5.

International cooperation, however, represents the most enduring success in terrorism prevention and disruption. United Nations Security Council Resolution 1373 (2001)[xi], which established global counterterrorism measures, and the expansion of the FATF regime[xii] to combat terrorist financing, gave rise to a multilateral cooperation infrastructure that remains in place today. The relevance of this point lies in how it reshaped the global paradigm of international security cooperation after 9/11.

3. CURRENT STATE OF THE PHENOMENON

Far from eradicating terrorism, it can be argued that the Western response actually drove its transformation, particularly in its jihadist strand, giving rise to regional franchises such as ISIS-Khorasan, Al-Shabaab, and JNIM in the Sahel[xiii], a phenomenon largely explained by the invasions of Afghanistan in 2001 and Iraq in 2003. The absence of centralized coordination forced terrorists to implement new mechanisms capable of withstanding U.S. military pressure, such as the radicalization of young people from Western countries, “lone wolf” attacks, and the use of simpler weapons, such as knives and vehicles. This not only represented a shift in the nature of the threat at the global level but also made the prevention of terrorist acts more complex[xiv].

Twenty-five years on, and despite the emergence of new terrorist groups, the phenomenon has lost centrality on the Western security agenda, displaced by great-power competition. This displacement coexists with counterterrorism organizations whose policies remain focused on immediate security and on preventing attacks through the recognition of behavioral patterns. The combination of both factors makes it impossible to address the social and economic conditions that allow terrorism to expand as a flexible political strategy, adaptable to multiple causes and, therefore, harder to contain.

The advance of artificial intelligence and social media has transformed contemporary terrorism, have accelerated radicalization processes and driving new extremist threats. Online radicalization timelines have dropped drastically, from an average of 18 months in 2005 to just a couple of weeks in 2026[xv]. This finds its most critical expression in far-right terrorism driven by “accelerationism” and SIEGE culture, ideologies that seek the collapse of democratic society through extreme racial violence[xvi]. By operating through decentralized digital propaganda, this generates an autonomous and unpredictable model of terrorism.

4. IMPLICATIONS FOR CHILE

Although geographically distant from the attacks that triggered the “Global War on Terror,” Chile incorporated into its legislation and institutions part of the security architecture that 9/11 set in motion in the West. In this regard, the country implemented initiatives in the financial, intelligence, and legal spheres; three areas in which the legacy of the terrorist attacks became durably embedded.

The first initiative involved the adoption of international financial standards. The recommendations that emerged after 9/11 gradually became a mandatory reference for national regulatory frameworks. In this regard, Chile adopted special recommendations against terrorist financing issued by the FATF through Law 19,913 and created the Financial Analysis Unit (UAF) in 2003[xvii], which subjected an extensive list of entities to the obligation of reporting suspicious transactions.

The second was the institutionalization of a state intelligence body. In Chile’s case, this process materialized in Law 19,974, enacted in 2004, which created the National Intelligence Agency (ANI)[xviii]. In its original wording, the law tasked the Agency with implementing intelligence measures to detect, neutralize, and counter the actions of national and international terrorist groups. Subsequent reforms diluted this specific function within a broader set of powers that today encompasses cybersecurity, critical infrastructure, and new data-access authorities[xix].

The third measure was the replacement of Law 18,314, in force since 1984, with new anti-terrorism legislation that would align national regulations with the international standards that emerged after 9/11. This process culminated in Law 21,732, enacted in February 2025[xx], which repeals the previous legislation and, among other aspects, updates the definition of the crime of terrorism.

Taken together, these legal and institutional developments demonstrate how the legacy of 9/11 is, in a certain sense, reflected in Chile through the implementation of new financial standards, the creation of an intelligence body with functions that help address the phenomenon of terrorism, and new legislation that confronts the phenomenon.

Figure 3. Pillars of legal and institutional adaption in Chile

Source: Own elaboration based on national legislation (Laws No. 19,913, 19,974, and 21,732).

5. CONCLUSIONS

Based on the foregoing, two conclusions can be drawn regarding the legacy of 9/11. The first concerns the strategic logic of contemporary terrorism, and the second concerns the institutional effects of the Western response.

First, terrorism continues to confirm the structural asymmetry that Kydd and Walter identify in their costly-signaling model, according to which an actor with marginal resources can force a more powerful state to incur disproportionate costs without eliminating the causes that gave rise to the violence in the first place. That asymmetry, which has persisted beyond the fragmentation of Al-Qaeda and the elimination of its leaders, has shifted toward new decentralized jihadist actors who replicate the same logic of provocation.

Second, the legacy of 9/11 can also be observed in the permanent expansion of the issues that states consider matters of national security. This phenomenon, which arose because of the war on terror, today shapes the frameworks used to classify other phenomena of political and social violence that are presumed to affect national security.

ALEJANDRO AMIGO
Senior Researcher

MICAELA TRAMER
Research Intern

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[i] Crenshaw, Martha. “The Causes of Terrorism.” Comparative Politics 13, no. 4, 1981.

[ii] Mulaj, Klejda, ed. Violent Non-State Actors in World Politics. New York: Columbia University Press, 2010.

[iii] Hoffman, Bruce. Inside Terrorism. New York: Columbia University Press, 2006.

[iv] Schmid, Alex P. Defining Terrorism. International Centre for Counter-Terrorism (ICCT), 2023. https://icct.nl/publication/defining-terrorism

[v] Kydd, Andrew H., and Barbara F. Walter. “The Strategies of Terrorism.” International Security 31, no. 1, 2006. https://www.belfercenter.org/sites/default/files/pantheon_files/files/publication/is3101_pp049-080_kydd_walter.pdf

[vi] Schmid, Alex P. Defining Terrorism.

[vii] Europol. European Union Terrorism Situation and Trend Report 2023. Luxembourg: Publications Office of the European Union, 2023.

[viii] Kimball, Jill. “Costs of the 20-Year War on Terror: $8 Trillion and 900,000 Deaths.” Brown University News, September 1, 2021. https://www.brown.edu/news/2021-09-01/costsofwar

[ix] Institute for Economics & Peace. Global Terrorism Index 2026. Sydney: Institute for Economics & Peace, 2026.

[x] Mueller, John, and Mark G. Stewart. Terror, Security and Money: Balancing the Risks, Benefits, and Costs of Homeland Security. Oxford: Oxford University Press, 2011.

[xi] United Nations Security Council. “Resolution 1373” (2001). S/RES/1373, September 28, 2001.

[xii] Financial Action Task Force (FATF). “History of the FATF.” Accessed September 8, 2026. https://www.fatf-gafi.org/en/the-fatf/what-we-do.html

[xiii] National Consortium for the Study of Terrorism and Responses to Terrorism (START). “Global Terrorism Database.” Processed by Our World in Data, 2022.

[xiv] Mohamed Taib. “Muslim Extremism after Two Decades of the ‘Global War on Terror.'” Academia.sg, 2021. https://www.academia.sg/academic-views/muslim-extremism-after-two-decades-of-the-global-war-on-terror/

[xv] Institute for Economics & Peace. “Global Terrorism Index 2026.”

[xvi] Europol. TE-SAT Report, 45.

[xvii] Ley 19913, que crea la Unidad de Análisis Financiero y modifica diversas disposiciones en materia de lavado y blanqueo de activos [Creates the Financial Intelligence Unit and Modifies Various Provisions Regarding Money Laundering]. Diario Oficial de la República de Chile, december 18, 2003. https://www.bcn.cl/leychile/navegar?idNorma=219119

[xviii] Ley 19974, sobre el Sistema de Inteligencia del Estado y crea la Agencia Nacional de Inteligencia [On the State Intelligence System and Creates the National Intelligence Agency]. Diario Oficial de la República de Chile, october 2, 2004. https://www.bcn.cl/leychile/navegar?idNorma=230999

[xix] Ley 21821, Fortalece y Moderniza el Sistema de Inteligencia del Estado [Strengthens and Modernizes the State Intelligence System]. May 30, 2026. https://bcn.cl/xe83Sx

[xx] “Chile cuenta con nueva Ley Antiterrorista: Estos son sus principales contenidos” [Chile Has a New Anti-Terrorist Law: These Are Its Main Contents], 2024. https://www.gob.cl/noticias/chile-tiene-nueva-ley-antiterrorista-conoce-principales-contenidos/