ISIS has sought to extend its reach globally, with an ISIS affiliate claiming credit for the recent downing of a Russian passenger plane over Egypt and a bombing in Lebanon that killed more than 40 people this week.
The Paris carnage has left at least 129 dead
-- including at least 80 at the Bataclan concert venue in the center of the city.
With a steady flow of radicalized foreign fighters traveling to places such as Syria and then returning -- in addition to the considerable number of homegrown ISIS sympathizers in many European countries -- the militant Islamic organization is finding it easier to support and encourage these kind of attacks, experts say.
"The French are overwhelmed by the numbers of people they're having to monitor," CNN terrorism analyst Paul Cruickshank said.
"They've opened surveillance files into more than 5,000 Islamic extremists throughout the country. There have been more than 1,000 French nationals traveling to Syria and Iraq. They know of 250 that have come back, and that's just the number they're aware of."
He pointed to a January terror plot thwarted in Belgium
when security services uncovered a huge cache of weapons -- as well as police uniforms -- suggesting a possible attack on a sensitive site there.
"Intelligence officials there and in the United States have told me that plot was directed by the top leadership of ISIS in Syria," he said.
"This is a group that is increasingly getting into the international terrorism business. I think all these different events of the past few weeks have really illustrated this: More than 100 killed during an attack in Ankara
-- ISIS suicide bombers -- the attack in Beirut
, 40 to 50 killed, ISIS bombers that claim for taking down that Russian Metrojet airliner
. It goes on. ISIS is pivoting toward international terrorism."
The fact the attacks in Paris all happened within 30 minutes suggested it was long-planned and there was some kind of command and control structure, according to Michael Weiss, co-author of "ISIS: Inside the Army of Terror."
"That's not to say it's coming out of ISIS headquarters in Raqqa," he told CNN. "One of the things to keep in mind is the that the caliphate has expanded in a way that many have not foreseen. It's not necessarily taking up more terrain in Syria and Iraq, but it is getting these affiliates -- getting these sleepers -- essentially to declare allegiance and to conduct their own operations."
While the gunmen and bombers picked a number of "softer" targets in the French capital -- a concert hall and restaurants -- other analysts said they believe the attack on the Stade de France was the real statement of intent.
"There's a tremendous amount of symbolism when you have France playing Germany -- this is the national sport of France, this is where you'll have a tremendous number of people gathered there and watching on television, hearing the explosions go off," CNN political commentator Buck Sexton said.
"To explode suicide vests outside of there is really to strike at the heart of France when the entire country is watching. The entire country heard those explosions as they went off. They would have thought, 'What was that?' So as soon as the news started to break, there would have been a ripple effect."
Cruickshank said the next challenge was the emergence of a major ISIS propaganda video if they eventually do take credit for the Paris attacks.
"Just recently, they (ISIS) instructed all their recruits, all their operatives on the ground, to film everything," he said. "They say there's no point launching these kinds of attacks if you don't film them."
So how will France react?
According to Sexton, there will be a "quite a response" from France. "They're already done airstrikes in Iraq and Syria. They'll go with more of that I think. There's also a U.S. presence on the ground in Syria -- that will likely increase."
He said France has shown it is capable of unleashing its fury.
And it is exactly the tone President Francois Hollande has taken.
Speaking from outside the Bataclan concert hall late Friday, he vowed France would be "ruthless" in its response