Peter Bergen is CNN's national security analyst, a vice president at New America and a professor of practice at Arizona State University. He is the author of " United States of Jihad: Investigating America's Homegrown Terrorists ." This article has been updated to include December's attack in Berlin.

(CNN) It used to be that we worried about truck bombs. Now we have to worry about trucks used as weapons.

The tactic has been adopted by jihadist terrorists in the West, including in the United States, but fortunately the lethality of these attacks had been relatively low -- until July's attack in Nice that killed at least 84.

In December, 12 people were killed when a tractor-trailor plowed into a crowd at a Berlin Christmas market , in an act that ISIS claimed it inspired.

The tactic has been a long time coming.

Al Qaeda's Yemeni branch encouraged its recruits in the West in its 2010 webzine, Inspire, to use trucks as a weapon. An article headlined "The Ultimate Mowing Machine" called for deploying a pickup truck as a "mowing machine, not to mow grass but mow down the enemies of Allah."

In September 2014, an ISIS spokesman similarly encouraged such attacks, saying of ISIS' enemies, "run him over with your car."

A month later, on October 20, 2014 Canadian Martin Rouleau Couture, who had traveled to Turkey in what appears to have been an unsuccessful attempt to join ISIS in neighboring Syria, ran over two soldiers in Quebec, killing one and injuring another.

according to the BBC. Also in 2014, there were two such car attacks in France in the cities of Nantes and Dijon, though the motives of the attackers, one of whom shouted "Allah Akbar!" after one of the attacks, are murky. In both cases the assailants had long histories of mental illness,according to the BBC.

The tactic has also been used in the United States. In 2006, Mohammed Taheri-azar, an American-Iranian, drove an SUV into an area crowded with students at the University of North Carolina at Chapel Hill. He later said that that the United States government had been "killing his people across the sea" and he was taking revenge and he was "thankful for the opportunity to spread the will of Allah." Luckily the attack killed no one but it did injure nine.

A year later, a pair of British terrorists opposed to the Iraq war rammed their Jeep into the arrivals area of Glasgow Airport, but killed no one.

The technique of using vehicles as weapons has been frequently employed by Palestinian terrorists targeting Israeli citizens.

We don't know enough yet to say what prompted the Nice attack. But what the attack shows is that we are now in an era when lone terrorists are becoming increasingly lethal.

Recall the attack at the Orlando nightclub that killed 49 in June carried out by a single gunman, Omar Mateen.

Until the Nice attack, the most lethal terrorist attack in the West carried out by a lone terrorist was by Anders Breivik, a Norwegian neo-Nazi who killed 77 people in 2011.

(Timothy McVeigh killed 168 people at the Murrah Federal Building in Oklahoma City with a truck bomb in 1995, but he was aided in every respect of the attack by co-conspirator Terry Nichols who is now serving a life term. There is no indication so far that the Nice attacker operated as part of a terrorist group.)

This will have important implications for how we conceive of the danger of lone terrorists in the West going forward. Law enforcement authorities in the States and other Western countries will have to consider the vulnerabilities to vehicular attacks of large, packed crowds of the kind that we saw jamming the waterfront in Nice celebrating their national holiday on Thursday.