Well-armed gunmen attacked six different locations across Paris on Friday night in one of the most horrific terrorist attacks in French history. Suicide bombs exploded outside of the Stade de France, attackers stormed Le Carillon — a popular restaurant — and hundreds were taken hostage at the Bataclan theater, where they were then summarily executed.

More than 120 people were killed and dozens more wounded, leading French President François Hollande to call the attacks “an act of war.”

The assaults, now claimed by the Islamic State, were jarring in scale and managed to roll elements from 15 years’ worth of terrorist attacks — including the Moscow theater siege in 2002 and the Mumbai attacks in 2008 — into one violent incident.

“This was basically a perfect storm of the worst kind of terrorist tactics combined with the most permissive of environments,” said Bruce Hoffman, the director of Georgetown University’s security studies program.

Hoffman added that Paris, compared with most cities, is considered well-prepared after putting security measures in place over the past two decades and especially after the smaller scale Charlie Hebdo attacks earlier this year.

“They attacked in one of the hardest places to strike,” Hoffman said. “And it was like a knife going through butter.”

At first glance, the attacks Friday night most resembled the Mumbai terrorist attacks in 2008, as they involved a number of gunmen attacking numerous “soft” targets spread throughout a relatively small urban area.

During the Mumbai attacks, Islamic terrorists stormed a number of high-end hotels and restaurants using Kalashnikovs and explosives — including suicide explosive vests. The attacks lasted four days and killed more than 160 people.

After the 2008 attacks, former al-Qaeda leader Osama bin Laden called for al-Qaeda and its affiliates to emulate Mumbai, but to no avail.

“At the time, the calls fell on deaf ears because no one was capable of carrying them out,” Hoffman said. “But now we have ISIS.”

Using the Mumbai model, the Paris attackers also seemingly borrowed from the London suicide bombings in 2005. While the attackers did not hit the city’s mass transit — as the London bombers did (three trains and a double-decker bus were targeted) — they used suicide vests in multiple standalone attacks outside the Stade de France. These explosions appeared to initiate the rest of the assaults. The other gunmen in Paris, however, also were reportedly wearing suicide vests solely to inflict as many casualties as possible prior to being killed.

A short time after the explosions outside of the Stade de France, gunmen stormed an Eagles of Death Metal concert at the historic Le Bataclan concert hall, taking hundreds hostage while others managed to flee in the ensuing chaos — including the band. Police raided the theater within a few hours, working quickly as the gunmen were reportedly executing concertgoers.

The police’s rapid response is a far cry from a similar theater siege in Moscow 2002, where Chechen terrorists took more than 800 people hostage at the Dubrovka theater. The Chechens made a number of demands to the Russian government and executed two hostages over the course of a multi-day siege before Russian special forces pumped an unknown gas into the concert venue. The Chechens were subsequently knocked unconscious and killed, while adverse effects from the gas also killed 100 hostages.

According to Hoffman, while the Paris attacks had characteristics of the incidents in Mumbai, London and Moscow, what stood out in Paris was the newfound capabilities of those who participated in the attacks.

“With the return of foreign fighters from Syria and Iraq, you basically have a different category of terrorists now,” Hoffman said, adding that France has sent more the 2,500 people to fight in the two countries. “You have hardened combat veterans that can take orders, work in units and are completely suicidal.”