What the World’s Terrorist Groups Have in Common

Teaching Resources—Terrorism: Introduction (including lesson plan with slides)
Higher Education Discussion Guide

Terrorism isn’t limited to one group, geographic area, grievance, goal, method, or era. Terrorists have committed violence for all kinds of reasons: to create a new country, carry out a revolution, pursue racist goals, free animals from laboratory testing, end access to abortion, and more.

It might, therefore, seem odd that groups with such diverse aims can all be classified as terrorists. What unites them? One commonality is that strong ideological beliefs drive them to commit violence.

What is terrorism?

In part because terrorism encompasses a range of acts and motivations, the term has a long and contentious history. Yet it’s not impossible to define. Generally, terrorism is understood to be violence, usually against civilians, committed by people or groups motivated by precise political and ideological objectives. Terrorists seek to achieve their goals while also inspiring fear and psychological terror in victims and bystanders. Terrorism isn’t just a crime—it’s political, and generally not undertaken for financial gain. And it isn’t war—it’s committed against civilians or other targets by state or nonstate actors (any person or group unrelated to a government).

What are the main ideologies behind terrorist groups?

Analyzing terrorist groups—where they come from, why they form, and what they hope to achieve—is the first step toward combating them. Scholars and practitioners take various approaches to categorizing and analyzing groups to recognize patterns of behavior, locate geographic hotspots and potential targets, and understand the evolution of groups over time. One prominent way is by ideology: the guiding principles, beliefs, and motivations that drive terrorist behavior. 

Why is it difficult to categorize terrorist groups?

Terrorist groups can be classified in different ways. Some categories currently used to group terrorists include violent actors committed to ethno-nationalist claims (groups seeking to control independent territory based on ethnic and nationalist identity claims), left wing extremist groups (those often driven by anti-capitalist, Marxist ideas), right-wing extremist groups (those often driven by neo-Nazi or neo-Fascist ideals), and religious extremist groups (groups motivated by an extreme and interpretation of faith).

But these categories are neither exhaustive nor mutually exclusive. Groups operate outside these ideological boxes: animal rights groups for instance, or environmentally minded ones are sometimes driven to ideologically-motivated violence. And terrorist groups can observe more than one ideology. For example, Euskadi Ta Askatasuna (ETA) is a group that fought for autonomy and independence for Basque people in Europe. As a group that also embraced Marxism, ETA can be described both as an ethno-nationalist and a left-wing group.

Despite the fact that much of today’s terrorist activity occurs in specific regions of the world, these categories do not stop at geographical borders. For example, while some religious terrorist groups have originated from those acting on an extreme interpretation of Islam, often originating from organized groups in the Middle East, these threats can come from other religions and regions around the world. For example, Japanese doomsday group Aum Shinrikyo killed dozens in a 1995 sarin gas attack at the behest of its religious leader.

And not every terror attack is conducted by a formal group or organization. Individuals could be radicalized by ideologies promoted by terrorist groups through the internet and other forms of media. 

Additionally, some people use the term "violent extremism" to describe terror attacks. It’s a broader term than terrorism that is not restricted to specific regions, nationalities, or ideologies, and can refer to ideology that has not yet resulted in violence, but may risk resulting in violence. While there is no universally agreed upon definition, governments often work to counter terrorism and violent extremism (the UN Office of the High Commissioner of Human Rights, for example, leads a combined strategy for “Terrorism and Violent Extremism”).

Explore examples of terrorist groups throughout history

With these categories—and caveats—in mind, take a look at several groups from around the world that meet these ideological criteria in the interactive above. This list contains just a few groups, representing a range of backgrounds, objectives, and tactics common in terrorism over the past fifty or so years.