Terrorism isn’t limited to one group, geographic area, grievance, goal, method, or era. For the last century, terrorists have committed violence for all kinds of reasons: to create a new country, carry out a revolution, achieve racist goals, free animals from laboratory testing, end 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.

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 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 nonstate actors (any person or group unrelated to a government) with fewer resources and less power than the state.

Analyzing terrorist groups—where they come from, why they form, and what they hope to achieve—is the first step toward combating them. Scholars 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. 

Terrorist groups fall into four broad ideological categories.

  • Ethno-nationalist groups. Ethno-nationalist terrorists claim to represent a specific ethnic or cultural group, often a minority. Distinct in that they seek to control independent territory, sometimes a separate country, ethno-nationalist groups tend to commit violence against their so-called rivals, often individuals belonging to a majority. Their grievances stem from what they characterize as oppressive action (or inaction) on the part of the government and/or the majority population. 
  • Left-wing groups. Driven by anti-capitalist, Marxist ideas, left-wing terrorists typically aim to overthrow capitalist governments they view as corrupt, elitist, and oppressive. Unlike ethno-nationalist groups, left-wing ones do not advocate for a specific subset of the population but argue that their struggle against capitalism and the state will result in egalitarian benefits for the people at large.
  • Right-wing groups. Right-wing groups define themselves in opposition to specific ideas and people they seek to destroy. They tend to be some combination of nationalist, racist, white supremacist, xenophobic, anti-democratic, anti-Semitic, anti-communist, and anti-government. Often, they have (Christian) religious leanings, favor the military, and fight to preserve the status quo. On the surface, right-wing groups seem like ethno-nationalist ones; the main difference is that instead of fighting for generally marginalized groups, right-wing groups threaten them, up to and including with murder.
  • Religious-oriented groups. Religious-oriented groups operate on an extreme interpretation of faith. Fervent religious motivations distinguish these groups, whose members tend to believe they are special, even chosen—and superior to those who don’t share their faith, or simply their version of it. Because religiously motivated terrorists often believe that they are obligated to commit violence by faith, and that this violence will lead to salvation, it can be more challenging to curb their violence.

A few caveats: first, these four categories are neither exhaustive nor mutually exclusive. Groups operate outside these ideological boxes: animal rights groups for instance, or environmentally minded ones. And terrorist groups often observe more than one ideology. For example, ETA, described below, 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.

Second, despite the fact that much of today’s terrorist activity occurs in specific regions of the world, these categories know no geographical borders. For example, while many religious threats have come from those acting on an extreme interpretation of Islam, often based in the Middle East, Japanese doomsday group Aum Shinrikyo killed dozens in a 1995 sarin gas attack at the behest of its religious leader.

Third, 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. 

With these categories—and caveats—in mind, let’s take a look at several groups from around the world that meet these ideological criteria. Remember: 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.

Terrorist Groups and Categories

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