What Does the Recent Spate of Lone Wolf Terrorist Attacks Mean?


Ramón Spaaij, Understanding Lone Wolf Terrorism: Global Patterns, Motivations and Prevention (Springer, 2012)


North American interest in lone-wolf terrorism is at an all-time high following several high-profile incidents. Two fatal attacks carried out against Canadian soldiers on October 20 and 22—with the second attacker actually able to enter the parliament building—were immediately followed by an unprovoked assault on New York City Police Department officers by a man wielding a hatchet. NYPD commissioner Bill Bratton has described the event as a terrorist attack.

Is lone wolf terrorism increasing? Does lone wolf terrorism pose, as some security experts claim, the “greatest threat” to the West? Though the intensity with which these questions are being asked has peaked, the questions themselves aren’t new. There remains a dearth of academic work on the topic, and Ramón Spaaij’s volume, Understanding Lone Wolf Terrorism: Global Patterns, Motivations and Prevention, is an important work that should help to inform the present discussion.

The biggest virtue of Spaaij’s work is that it provides a quantitative look at lone wolf terrorism across fifteen Western countries. This empirical approach can assist anyone concerned about the most recent incidents to assess them in light of historical patterns. The database of lone wolf terrorists Spaaij draws his conclusions from consists of 88 individuals who carried out a total of 198 attacks between 1968 and 2010. However, one limitation in Spaaij’s data should be noted: Although his book was published following the deadliest lone wolf terrorist attack in history—Anders Behring Breivik’s 2011 attack in Norway that claimed 77 lives—it is not included in Spaaij’s dataset. If Breivik were included, the patterns Spaaij identifies would shift somewhat. For context, the second deadliest lone wolf terrorist, Joseph Paul Franklin, killed only 18 people (in multiple attacks). Spaaij’s conclusions are nonetheless quite valuable—and indeed, one could reasonably argue that it’s better to see the data without Breivik included, since his case represents such an outlier.

What does Spaaij’s data reveal? A few points that he makes can put the most recent incidents into some perspective.

Lone wolf terrorism is increasing. Because of the relatively small universe of data (an average of fewer than five lone wolf attacks per year), there have naturally been extreme fluctuations from one year to another. However, such statistical anomalies are reduced if one examines this phenomenon from one decade to the next. Doing so reveals that, beginning in the 1970s, there has been a gradual yet observable increase in the United States and a much more rapid increase outside the United States. Spaaij notes that “between the 1970s and 2000s, the total number of lone wolf terrorist attacks per decade rose by 45% (from 22 to 32) in the United States and by a massive 412% (from 8 to 41) in the other 14 countries combined.”

Despite this observable increase, the overall number of lone wolf attacks remains low. During the entire period Spaaij examines, the average number of lone wolf attacks per year was 4.7—which illustrates how significant, and how unusual, it would be to have three such attacks in a four-day period. But given the trend toward increased lone wolf terrorism over time, the annual average of lone wolf attacks by the 2000s had reached 7.3.

Overall, between 1968 and 2010, lone wolf attacks accounted for about 1.8% of all terrorist incidents.

Lone wolf attacks are harder to stop, but tend to be less deadly, than those planned and executed by groups. Many commentators have noted how difficult it is to prevent lone wolf terrorist attacks. This is true: A group involved in a terrorist plot can be charged with terrorist conspiracy even if all the overt actions they had taken in preparation of the attack would otherwise be legal. Thus, a country dedicated t0 preventive policing has a decent chance of disrupting group plots. In contrast, an individual cannot, by definition, conspire with himself. As a result, even if authorities know that an individual poses a danger (as Canadian authorities suspected about both attackers who struck in their country), it may be difficult or impossible to stop him from carrying out a lone wolf attack.

Though lone wolf terrorists have an advantage in avoiding the disruption of their plots by authorities, their attacks tend to be less lethal than those of multiple attackers working in concert. Spaaij notes that while lone wolf terrorism averaged 0.62 deaths per incident during the period in question, all terrorist attacks in the countries studies averaged 1.6 deaths per incident. Moreover, while terrorism has become increasingly lethal, lone wolf attacks remained unchanged in that regard. Though Breivik’s devastating attack would push the lone wolf trend upward if it were included in Spaaij’s data, it wouldn’t have been enough to make lone wolf attacks equal to all attacks in lethality. Further, the three most recent attacks averaged 0.67 fatalities per incident, consistent with historical patterns.

Lone wolf attackers are inspired by diverse ideologies, but jihadist motivations are increasing. Spaaij analyzes the lone wolf attackers he studied by motive:

  • Right-wing extremism-white supremacy: 17%
  • Islamism: 15%
  • Anti-abortion: 8%
  • Nationalism/separatism: 7%

Of these, he notes that the recent trend had been toward an increasing number of attackers with Islamist motivations. Part of the reason for this increase in Islamist-inspired lone wolf attacks may be the general increase in Islamist terrorism; and Spaaij further notes that these attackers may have been responding in part “to the call by al-Qaeda ideologues for individual jihad.” Spaaij’s book was written before the Islamic State of Iraq and the Levant (ISIL) was expelled from al-Qaeda, but that group has also made similar calls.

Lone wolves are more likely than other terrorists to be mentally ill. Mental illness is not a compelling root-cause explanation for terrorism: As Marc Sageman has noted, terrorists’ mental health tends to be “surprisingly normal.” However, Spaaij writes that lone wolves “tend to have a greater propensity to suffer mental health issues” than do individuals involved in group terrorism. He concedes that it is difficult to analyze the mental health of lone wolves with precision, but describes these lone actors as “relatively likely to suffer from some form of personality disorder.” Indeed, Spaaij provides five case studies of lone wolves’ mental state, and four of the five examined were diagnosed with personality disorders; four of the five also seemingly suffered from depression. Spaaij’s findings are consistent with other academic treatments of lone wolf terrorism and mental illness.

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Spaaij notes that the growth of lone wolf terrorism over time may in part be attributable to “the increased prevalence of the Internet as a vehicle through which to disseminate extreme ideologies.” The Internet is a powerful medium that has changed the impact of communications in multiple ways, and the Islamic State’s much-celebrated social media savvy may be part of the reason we’re seeing a sudden spike in lone wolf cases. We also shouldn’t leave our own media’s coverage of the Islamic State out of the discussion: The more we portray it as an unstoppable force, or portray lone wolf attacks that cause few fatalities as devastating to our psyche, the more it may encourage copycats. The increase in school shootings following the 1998 massacre in Littleton, Colorado is one example of this phenomenon.

There is, ultimately, no easy answer to lone wolf terrorism, just as there isn’t an easy answer to the growing role that violent non-state actors are playing in the world. Getting reliable data on the phenomenon of homegrown lone wolf terrorism is an important part of fashioning a response, and Spaaij’s volume makes an undeniable contribution.


Daveed Gartenstein-Ross is a senior fellow at the Foundation for Defense of Democracies and an adjunct assistant professor in Georgetown University’s security studies program. He is the author or volume editor of fifteen books and monographs, most recently China’s Post-2014 Role in Afghanistan.