What is Terrorism? The Defining Elements of an Evolving Concept

What is Terrorism? The Defining Elements of an Evolving Concept

Morgan Demboski

Government officials, law enforcement, and scholars have long struggled to come up with an internationally accepted definition of terrorism. The term is a very ambiguous one – what is terrorism and who is a terrorist depends entirely on the subjective view of the definer. As Petra Bartosiewicz says in her TedTalk, the definition of a terrorist is “the enemy of a state, as defined by the state.” But some states, like the U.S., can’t even agree on a single national definition. In fact, almost every U.S. federal agency has a different definition of terrorism that reflects its specific priorities and interests, leading to over 20 definitions of terrorism just used by the U.S. government.

Though there are probably hundreds of definitions for the term, they generally all share a couple of key elements that have come to characterize the concept we call terrorism.

To understand the fundamental characteristics of terrorism, it is important to first understand how the term – and the act of terrorism itself – has changed throughout history.

Terrorism first derived from the “regime de la terreur” during the French Revolution in which the new revolutionary state used terror as an instrument of governance to exert power and intimidate political opponents and dissidents. Eventually, the term took on a different meaning, transitioning from a concept associated with the abuse of office and power to one associated with violent actions of non-state actors. Initially drafted by David Rapoport [PDF], modern terrorism can be divided into four overlapping waves:

Walls, E. (2017). Waves of Modern Terrorism: Examining the Past and Predicting the Future [Table 1]. Georgetown University-Graduate School of Arts & Sciences.
1. The Anarchist Wave

The first of these waves began in the late 1800’s and can be characterized as the Anarchist Wave, which is also commonly referred to as “The Golden Age of Assassination” since violent acts were directed mainly at government officials and leaders, not civilians. This wave was heavily influenced by the concept of “Propaganda by the Deed,” and it reached the U.S. when anarchist Leon Czolgosz assassinated President William McKinley in 1901. 

2. The Anti-Colonial Wave

The second wave of terrorism is known as the Anti-Colonial Wave, which began in the 1920s after the modern map of the Middle East and Central Asia was drawn during the Paris Peace Conference following WWI. It was characterized by terrorism in the service of national liberation and ethnic separatism, with groups often using violent means to rid themselves of foreign colonial rule and establish their own independent nations. This anti-colonial movement intensified after WWII when the weakening of European superpowers and technological advances in weaponry allowed several countries, such as Algeria and Israel, to gain national independence from colonial powers.

3. The New Left Wave

The third wave is known as the New Left Wave, which arose in the 1960s in opposition to the Vietnam War and was marked by widespread left-wing activism. It was during this wave that terrorism began to take on an international dimension, with the Palestine Liberation Organization (PLO) playing a major role in elevating terrorism to the global stage. Sometimes referred to as the ‘Golden Age of Hijackings,” this wave is when transnational transportation – like planes – became a popular attack vector for terrorist groups. 

4. The Religious Wave

The fourth wave, the age of Religious (Islamic) Terrorism, was set in motion by the Iranian Revolution in 1979 and is still ongoing. This wave was inspired in many places (e.g. Algeria, Chechnya, Indonesia) by the pan-Islamic dream of uniting fundamentalist Muslim states under caliphate hegemony and Sharia law, free from Western cultural contamination. 

5. A New Wave? 

Some (including myself) would say we are now entering a new wave of terrorism, which could be characterized as the age of the internet and technology. Online radicalization and cyber attacks have become two of the main focuses of law enforcement and policy in the 21st century. The modus operandi, recruitment techniques, and propaganda strategies of terrorist organizations have shifted due to social media and internet platforms where they are now able to reach a much larger audience. Terrorist attacks are increasingly being carried out by lone wolves and leaderless resistance networks rather than formally organized groups, and this trend has been further facilitated by the COVID-19 pandemic that has rapidly accelerated organizational decentralization. Even nation-states have jumped on the opportunity to use the internet to promote their goals, carrying out cyberattacks and disinformation campaigns to incapacitate enemy critical infrastructure and provoke wider public hysteria.

So now you know a brief history of terrorism. But what actually is it? Well, let’s go over some of the foundations.

Terrorism is an intrinsically political concept.

Simply, terrorism is fundamentally and inherently political. It is an act in which the goal is always to accomplish political goals, which include religious and ideological aims as well. These objectives could range from national liberation, to changing the current socioeconomic system, to revolution, to even anarchism (among many others). Characterizing terrorism as a political concept is critical in distinguishing it from other types of violence and is important to understanding its aims, motivations, and purposes.

Terrorism is a planned act almost always committed by rational actors who use – or threaten to use – violence to achieve their goals. 

Related to the essence of the activity itself, terrorism includes the use of, or the threat to use, violence against a target. This is an essential element because it excludes political phenomena, such as nonviolent protests, from being categorized as terrorism. Terrorism is a planned, calculated, and systematic act committed by rational-acting individuals, often belonging to an organization or movement dedicated to some sort of revolutionary change. Many have attempted to label terrorists as irrational, but this is severely misguided – terrorism is a deliberate act that is almost always the result of strategic thought. Terrorists as rational actors is an important aspect of terrorism research because it allows scholars to use game theory and strategic choice theory to make quantifiable predictions and conclusions regarding terroristic activities.

Terrorism can be categorized as unconventional warfare carried out by non-state entities, but nation-states can also sponsor terrorism or use terrorism as a tactic to achieve their goals.

 Terrorists are not bound by the established rules of warfare or codes of conduct. They operate at will and often aim to create a sense of insecurity and uncertainty amongst the general population through acts of “random violence” and “massive fear.” As mentioned earlier, the term “terrorism” first originated during the French Revolution as ‘regime de la terreur,’ used to describe the abuse of office and power by governments who used terror to manipulate their citizenry. Now, terrorism is commonly understood to be violent acts committed by non-state or sub-national actors. In his book “Inside Terrorism,” Bruce Hoffman states that this is an important differentiation because violent acts of a state against their own citizenry is generally termed “terror” while violent acts directed at civilians by non-state entities is termed “terrorism.” However, it should be noted that states can be involved in terrorism by providing support, encouragement, and assistance to sub-national terrorist organizations, which is often referred to as “state-sponsored terrorism.” Iran and Syria are two examples of countries widely known to sponsor terrorism through funds and resources and use terrorist groups as proxies in conflicts. 

Terrorist attacks are fundamentally designed to impact and/or influence an audience beyond the immediate target. 

Finally, what I believe to be one of the most characterizing elements of terrorism is its psychological dimension. Terrorist attacks are designed to have wide-reaching psychological repercussions that span beyond the immediate victim/target. In other words, terrorists want to invoke fear in an audience that is different or larger than the actual target of the violence. These attacks are, in a sense, symbolic and intended to coerce or intimidate a civilian population, to affect the conduct of a government, or to influence the policy of a government through coercion or intimidation. In my opinion, I believe this is a defining element of terrorism because when I think of all of the different types of terrorism, the methods various groups employ, and the victims that are targeted, one thing they all have in common is their ultimate goal to influence a wider, watching “target” audience. 

So as a recap… 

An equivocal term with no internationally agreed-upon definition, terrorism has evolved immensely in the past century, with the tactics, targets, and ideologies of terrorist groups shifting over time. There have been several waves of terrorism, each distinct from one another and exhibiting drastically different characteristics. However, all the divergent attacks from these waves share essential definitional elements that differentiate them from other forms of violence or political activism.

Terrorism involves a violent act committed with the goal of achieving political, religious, and/or ideological objectives. It is calculated and systematic, often committed by a rational actor who makes a strategic choice to commit violence to achieve their goals based on social conditions and perceived costs and benefits. Terrorism is, for the most part, committed by non-state entities, but other groups, such as nation-states or those technically regarded as guerrilla groups, can use terrorism as a tactic to achieve their goals. Finally, whether to sow fear and unrest in a general population or to invoke action from a government, terrorists always have the intent to influence a broader, “watching” audience. 

Inside scoop on how tPP decides whether a felony criminal case should be included in our dataset:

I know what you’re thinking: with all of this confusion and ambiguity surrounding terrorism, how does The Prosecution Project decide which cases should be included in the tPP dataset? Well, as a general rule, the tPP dataset aims to be inclusive of all cases that involve felony crimes with sociopolitical motivation, as stated by the perpetrator or labeled as such by official state bodies, such as law enforcement or federal agencies. As a result, tPP tracks more than just domestic terrorism cases in our database. In addition to other criteria, we generally determine whether a case should be included based on two questions:

Is the crime 1) in furtherance of terrorism, extremism, or political violence (excluding state-sanctioned), and/or, 2) in furtherance of the sustainability or advancement of the extremist/terrorist organization (e.g. FTO, DTO) (e.g. retaliatory killings as required by inter-group obligations), HVE network (e.g. purchasing weapons for group’s attack) or extremist movement (e.g. financial crimes to support Sovereign Citizens which the FBI defines as extremist movement)?


Are the groups, individuals, monikers, networks, movements and/or tactics involved in the case described in official State speech acts as terroristic, extremist/HVE, or intended to send a message on behalf of an ideology?

These questions provide us with a simple yes or no answer on whether to include the case, helping us to avoid the ambiguity that commonly surrounds instances of political violence (as exemplified above in the discussion of terrorism definitions).

Want more? Of course you do!

To learn more about tPP’s process and the information included in our dataset, check out our “tPP Includes…” page.

To read more about how the U.S. and the academic community define terrorism, take a look at the resources provided on tPP’s “Defining Terrorism” page.

Check out more tPP blog posts written by our members here!

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