Unlike the November assault in Paris and the twin airport bombings in Belgium and Turkey, Thursday’s attack in Nice, France, traded explosives and small arms for the lethality of a speeding box truck aimed at late-night revelers. With at least 84 reported killed and 52 critically injured, one man in a truck managed to kill more people than the attacks in San Bernardino, Calif., Chattanooga, Tenn., and Orlando did combined. That raises the question: How was a truck able to kill so many so quickly?

The answer consists of a confluence of factors, the primary one being that the venue the attacker singled out, the Promenade des Anglais, was a nearly indefensible target. A long stretch of seaside road and boardwalk, the promenade — packed with hundreds celebrating Bastille Day — would have been nearly impossible to police and to secure, said Bruce Hoffman, a counterterrorism expert and the director of Georgetown University’s Security Studies Program.

The evening was ending and security forces, on heightened alert following the European soccer championships and the religious holiday of Ramadan, had probably relaxed, letting their guard down as festivities concluded.

In addition, the method of attack was atypical to what security officials might have been expecting — a box truck rather than explosives or firearms. That added to the confusion and hampered any effort to stop the vehicle.

In this type of attack, Hoffman said, the planners deliberately choose a target where the crowd size and location delays the authorities’ response time. In this case, news reports indicated that the truck was able to drive more than a mile before the driver was shot and killed by police and that it took ambulances up to 25 minutes to respond to the scene. Grisly footage shot from cellphone cameras shows some people standing idly while others run as the truck accelerates into the crowd, reinforcing the notion that many had no clue they were being targeted. With no gunfire or explosives to run from, it’s easy to understand why people might have been caught off guard and slow to react.

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Like soccer stadiums, shopping malls and cafes, the promenade in Nice was what is often referred to as a “soft target” — a public place often difficult to protect because of its high profile, transient population and plethora of entry and exit points. Attacking soft targets has been the hallmark of modern terrorism, yet according to Hoffman, the attack in Nice could be a crucial step forward for the organizations that are trying to damage the fabric of liberal Western societies.

While no terror group has taken responsibility for the Nice attack, both al-Qaeda and the Islamic State have called for vehicular assaults against Western countries in the event that more conventional weapons are inaccessible. News reports, however, indicate that the truck in Nice was also loaded with small arms and explosives.

“That’s the message these groups are trying to push: ‘You’re never going to be safe.’ It’s a strategy they’ve been pushing the last few years, and unfortunately, now it’s being realized,” Hoffman said.

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Hoffman said the use of weapons and explosives in places like Paris and Brussels, combined with the vehicular attack in Nice, represents a tactic that involves inundating security forces with so many types of threats that they can’t possibly track and chase down every lead associated with them, thus allowing larger attacks to potentially slip through undetected.

“How can you impose on security personnel the ability to respond quickly enough to all these very different types of attacks?” Hoffman asked. “Have we crossed the threshold that we have to be on alert for every single event regardless of any outside circumstances?”

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