People offer tributes to the victims of Friday’s terror attack on the Promenade des Anglais in Nice, France.) (David Ramos/Getty Images)

The Bastille Day attack on throngs of people in the coastal city of Nice represented not the evolution of the terror threat, but its accelerating devolution.

Almost every aspect of the attack could be characterized as terror in its crudest form: the absence of explosives or other marks of meaningful preparation; the targeting of defenseless pedestrians packed onto a narrow parade route; the use of the most unassuming of vehicles — a delivery truck — as a weapon.

In some ways, that recognition of the lethal potential of a conventional means of transportation echoed the principal innovation of the Sept. 11, 2001, attacks that envisioned airplanes as missiles and ushered in the modern era of Islamist terror.

But nothing about Nice suggests it aspired to the Sept. 11 plot’s sophistication. It did not require years of training, extensive travel, significant funding, elaborate coordination or external communication.

Instead, French authorities now believe that the attacker was radicalized in a matter of days. An uncle of the driver of the truck in Nice told the Associated Press that his nephew had recently been influenced by an Algerian member of the Islamic State. And though there is no indication yet that the terror group was even aware of the plot, it issued a statement Saturday claiming the killer as one of its “soldiers.”

Like other recent attacks in Orlando, Istanbul, Brussels and Baghdad, the violence in Nice fits a widening pattern of brutal simplicity. Al-Qaeda’s obsession with the aesthetic aspects of terror have given way to the Islamic State’s embrace of the most primitive possible plots, all of them serving as inspirational examples to imitators with no apparent ties to either of those groups.

Nice “is in terms of sophistication pretty damn crude,” said Daniel Benjamin, a former State Department counterterrorism official now at Dartmouth College. The Islamic State and its imitators have “legitimated simple attacks and essentially discarded the notion that an attack has to be super sophisticated and outwit the West at its own game of high-security.”

The shift in approach, Benjamin said, has undermined the ability of security services to detect plots and “democratized terrorism in a way that is causing us an awful lot of grief.”

The attack in Nice, which killed 84 people and injured dozens of others, has yet to be linked to the Islamic State or al-Qaeda, but it tracks a do-it-yourself model of inflicting carnage that both organizations have advocated in recent years.

Indeed, al-Qaeda’s affiliate in Yemen proposed using a high-powered truck to bludgeon pedestrians in the second issue of its glossy, English-language magazine, Inspire, six years ago.

A section called “Open Source Jihad” included a full-page photo of a gleaming U.S.-built pickup, and urged the group’s followers in America to use such vehicles as “a mowing machine, not to mow grass but to mow down the enemies of Allah.”

It’s not clear that the driver in Nice, a 31-year-old French-Tunisian named Mohamed Lahouaiej Bouhlel, had ever seen that particular issue of Inspire.

If so, he did not bother with the more elaborate instructions in those pages to weld steel blades to the front of the vehicle. But his rampage did adhere to other suggestions in the article, which proposed finding a “pedestrian-only” location and listed France among the countries where the “idea could be implemented.”

Packed with vacationers celebrating Bastille Day, the seafront promenade in Nice fit the definition of a “soft” target that U.S. and Western security services have found extraordinarily difficult to protect.

Just hours before the attack in Nice, one of the United States’ top counterterrorism officials, Nicholas J. Rasmussen, warned that “we face more threats originating in more places and involving more individuals than at any period since 9/11.”

In testimony before the House Homeland Security Committee, Rasmussen said that the simplicity of the latest wave of plots has dramatically shortened the amount of time — the “flash to bang ratio,” as he put it — that officials have to detect them.

“The time between when an individual first decides to pursue violence and when an actual attack might occur has become extremely compressed, placing much greater pressure on law enforcement and intelligence,” Rasmussen said.

U.S. officials were already on high alert for domestic plots when Omar Mateen killed 49 people and wounded more than 53 others at the Pulse nightclub in Orlando last month.

The attacks in Belgium, Paris, Istanbul and Baghdad over the past year have employed a mix of firearms and explosives on other vulnerable targets including soccer stadiums, neighborhood markets, concert venues and the open spaces at the airport in Brussels where travelers could congregate without undergoing security checks.

U.S. counterterrorism officials warned this week that they were bracing for possible violence at political conventions that get underway this month, including the GOP event in Cleveland starting Monday that is expected to formally nominate Donald Trump as the Republican candidate for president.

“Anytime there is a national spotlight on a political event in the United States, there is a risk that groups that aspire to do just that, engage in acts of domestic terrorism, will be attracted,” FBI Director James B. Comey said in testimony at the same Thursday hearing.

The wave of attacks across western Europe and the United States over the past year, as well as a surge in immigration from Syria and other Arab nations, has contributed to a heated political climate that some security officials and experts believe only heightens the danger.

The timing of the Nice attack is expected to focus attention at the GOP convention on security issues, including Trump’s calls for bans on allowing Muslims to enter the United States.

Britain’s vote to leave the European Union last month also largely reflected an expanding nationalist impulse to exert greater control over the country’s borders. And tension in the wake of a series of terror attacks in France have fueled the rise of the right-wing party there led by Marine Le Pen.

Experts said that the tragedy in Nice is likely to add to an already highly pressurized political atmosphere that — combined with its potential to inspire militants who have not yet mobilized — amplifies the security threat.

“The consequences are really bad because expressions of anti-Muslim sentiment drive radicalization, drive more violence, drive more anti-Muslim sentiment,” Benjamin said. “This is as vicious a cycle as you can imagine.”

Julie Tate contributed to this report.