Updated on April 7, 2017

Shortly after a stolen delivery truck sliced through a crowd of shoppers in Stockholm on Friday, killing and injuring multiple people, Swedish Prime Minister Stefan Lofven assessed the carnage. “Sweden has been attacked,” he said. “Everything indicates an act of terror.” The terror, in this case, came in one of its crudest forms: a truck, a driver, and a crowd of people. An assailant had weaponized everyday life in a country of nearly 10 million people, 4.5 million cars, and countless public squares. The plan likely involved some level of sophistication; the attacker, for example, may have researched vulnerable venues ahead of the incident. But the nasty truth about violence so basic—requiring no training, weapons, or collaboration with a terrorist group, nothing more than access to a vehicle and the ability to drive it—is that it is extremely difficult to prevent. The less complex the terrorist plot, the harder it is to thwart.

The type of terrorism on display in Stockholm leaves societies with three choices: 1) Try to secure open spaces by heavily fortifying them, thus transforming people’s way of life; 2) Try to stop would-be attackers by dramatically expanding the government’s surveillance and investigatory powers, thus increasing the state’s intrusions into people’s lives; or 3) Try to minimize the frequency and lethality of terrorism, while learning to live with the threat of attacks and to be resilient when they inevitably occur. Those choices are lurking behind fierce debates in many European countries right now about how to better protect public places, control immigration, and balance privacy and security.

Terrorist groups, for their part, grasp the terrifying simplicity of violence by vehicle. Thomas Joscelyn, a terrorism expert at the Foundation for Defense of Democracies, points to an article titled “Just Terror Tactics” in an issue of ISIS’s Rumiyah magazine, which featured an image of a rental truck near photos of the Macy’s Thanksgiving Day Parade and last year’s Bastille Day truck attack in Nice, France:

“Though being an essential part of modern life, very few actually comprehend the deadly and destructive capability of the motor vehicle and its capacity of reaping large numbers of casualties if used in a premeditated manner,” the article in Rumiyah read. ...

“Vehicles are like knives, as they are extremely easy to acquire,” Rumiyah advised would-be jihadists. “But unlike knives, which if found in one’s possession can be a cause for suspicion, vehicles arouse absolutely no doubts due to their widespread use throughout the world.” ...

Rumiyah’s editors went on to suggest targets, including “outdoor markets.” “In general,” the Islamic State advised, “one should consider any outdoor attraction that draws large crowds.”

European governments facing a growing threat of Islamist terrorism, especially terrorism perpetrated by lone extremists inspired by groups like ISIS, “will now face even greater pressure to secure venues that were not designed to be secure, against a weapon that was not designed to be a weapon,” the Soufan Group, a security consultancy, wrote after a deadly truck attack in Berlin in 2016.

The Soufan Group elaborated on this observation in another brief last year:

Unlike symbolic or high-value targets such as government buildings, there is no way to truly harden soft targets. Parks are designed for leisure, and for easy access and movement. Mass transit is designed to move people efficiently. Both would cease to fulfill their designed functions if onerous security measures were implemented. Furthermore, adding security on the perimeter of a soft target simply changes the strike zone. Terrorists are looking for high body counts; a crowd at a checkpoint for a park or a metro is just as attractive as a crowd inside a park or metro. One needs to look no further than Iraq to see how dangerous crowded checkpoints can be for the civilians they are ostensibly designed to protect.

Terrorists have wielded vehicles as a weapon against civilians not just in Berlin and Nice and now, it seems, Stockholm, but at a chemical plant in France and on the campus of Ohio State University. The terrorism scholar Martha Crenshaw estimated after the Nice attack in 2016 that there had been 30 such incidents around the world since 1994, excluding attacks involving car or truck bombs (Palestinian terrorists have been deploying car-ramming against Israeli civilians for years). As the Soufan Group has written, “There is nothing new about terror strikes against soft targets; what is new is that the baseline threat is now so high in so many countries.”