If ISIS was telling the truth when it claimed responsibility for Friday's Paris terror attacks, then this represents a "major shift in ISIS's global strategy," according to Will McCants.

McCants is the director of the Brookings Institution's Project on US Relations With the Islamic World and the author of The ISIS Apocalypse — one of the best books to date on the group. I called him on Saturday to try to understand what lessons about ISIS we should draw from the Paris attacks if indeed the group is responsible as both it and the French government say.

McCants cautioned that we still don't know a lot about the Paris attacks. But in recent weeks, he says, ISIS has launched a suicide attack against an area in Lebanon where Hezbollah is strong. It's also suspected of bombing a Russian civilian airliner in Egypt. These attacks together, he says, suggest that ISIS is lashing out. It's been losing territory in Syria and Iraq, and this might be a response — an effort to deter further intervention against it by showing foreign powers that they'll pay a price.

If McCants is right, then the Paris attacks suggest that we could be at a watershed moment for ISIS. What follows is a transcript of our conversation, edited for length and clarity.

Zack Beauchamp: If the Paris attack was, as it seems, done by ISIS, what would this tell us about their strategy?

Will McCants: It would tell us that they are willing to hit their primary enemies in foreign places where they are most vulnerable, and note that all three of those attacks [Paris, Beirut, Russian airliner] were not on government sites. They were on civilians, they were all complex, and they were all high casualty.

If ISIS directed this plot in Paris, it's also a shift in its operational focus and capability. Before this, they had satisfied themselves with trying to inspire attacks. But anyone skilled who's abroad, they were primarily trying to attract them to Syria and Iraq for state building. This would suggest that they have changed their focus and are willing to direct more resources to foreign operations.

"They may have been developing this capability for quite some time, and it's only now that they are unleashing it"

Zack Beauchamp: Why would ISIS start devoting resources to international terrorism now, when previously it's focused much more on taking and holding territory in Syria and Iraq?

Will McCants: We can't know for sure. I can come up with some plausible reasons, but it's completely guesswork.

One type of explanation is that this is primarily about recruits and keeping momentum going. You could say that this is part of the broader struggle to displace al-Qaeda as the head of the global jihad — think of it as part of a competition with them for recruits. They've also been losing some territory, and are trying to mitigate those losses by focusing people's attention abroad with a mind to attracting recruits.

Another explanation is that they want to deter further military action against its strongholds in Syria and Iraq, so they are going after some of their primary enemies.

Or you could say that that they've had international terrorist intentions all along, but they never had the capability or the opportunity.

Any of those is plausible, so the challenge is for us trying to make sense of it on the outside. We just don't know what's going on in their own internal deliberation, and we might not know for years. If you look at the aftermath of 9/11, we didn't know exactly why they had undertaken those attacks for years.

Zack Beauchamp: Of those explanations that you've offered, which one do you think is the most plausible?

Will McCants: I guess if this were just about an attack in Europe, you might say that it is in reprisal for the attacks being carried out in Syria and Iraq. I don't see this as necessarily part of the propaganda effort or the war with al-Qaeda, because they've already succeeded in attracting far, far more recruits.

Given the target of a major enemy in Europe, in light of attacks on Russian civilians and an Iranian ally in Lebanon, it seems to me that this has to do with the war to expand its territory in Syria and Iraq. It is putting its major adversaries on notice that if they continue to impede its state building, they will pay a price.

"If we don't know why ISIS did these things, we risk making some major blunders that play into its hand"

Zack Beauchamp: ISIS has recently lost a fair amount of territory in Iraq and Syria. If this shift in strategy is real, is it born out of weakness?

Will McCants: I don't know that you could say it's weakness because they're still pretty strong. But they have lost something like 25 percent of their territory.

I think it has made the calculation that it can no longer pursue its expansion strategy in Syria and Iraq without changing the calculations of the enemies currently halting its expansion. These attacks would be a way of inflicting costs on them.

Zack Beauchamp: How reasonable a calculation on their part is this? French President François Hollande's rhetoric after the attack gives the impression that France is likely to intensify its bombing efforts in Syria and Iraq rather than scale them back.

Will McCants: Yeah. I think attacks like these are going to give France, Iran, Russia, and the United States common cause in curtailing the ISIS advance. Especially if these plots go back to ISIS central — if they have operatives that were trained and financed from headquarters in Raqqa.

I think those governments are going to determine enough is enough. They have had other priorities in the destruction of ISIS, and that might change their calculations. If that is the intent of ISIS, to deter them from further military action, I anticipate it will have failed because we are going to see a lot more military action against ISIS.

Zack Beauchamp: How would you want the French and American governments to think about their military response to this attack?

Will McCants: The challenge for governments in responding to this kind of stuff is to wait until you know exactly what your enemy is trying to provoke you to do. If we don't know why ISIS did these things, we risk making some major blunders that play into its hand.

Think about 9/11. Al-Qaeda told us vaguely in the propaganda, "You're the crusaders, and we want to get you out of here." But the real strategy behind the attacks wasn't revealed for a few years, and they came from internal al-Qaeda memoranda that later surfaced. In the aftermath of the 9/11 attacks, we didn't understand then that Al-Qaeda was dearly hoping for a large military deployment so that it could bog us down and win this propaganda war.

We made the right decision early on — that went against al-Qaeda — by going in Afghanistan. But we made a different decision in Iraq, and it played into their hands. There's a similar worry here, and without knowing exactly why ISIS undertook these attacks, we risk dancing to their tune.

"We're not talking about al-Qaeda hiding out in Pakistan. We're talking about an actual government that has money to put behind plots and has very motivated people, many of them with European passports."

Zack Beauchamp: You mentioned earlier that it's not obvious that this was planned from ISIS headquarters. This seems like a very sophisticated attack. How do you assess the likelihood that this was centrally planned versus something that ISIS sympathizers in and around Paris set up on their own?

Will McCants: Because it's so complicated, both in terms of the timing and coordination, it goes against the idea that these were just some guys who decided to pick up weapons and wreak havoc. It strongly suggests some training abroad, at least by some of the members, if not direct coordination.

I'm also mindful, Zack, that this comes at the end of two weeks where we have seen two other high-profile, high-casualty, complex attacks on Russia with the airliner and on Hezbollah with the attack in Beirut. One guy in Beirut whose suicide bomb failed to detonate said that he was sent there by ISIS directly. That history — together, then, with the complexity of the Paris attacks — suggests to me that ISIS Central has a guiding hand in this.

But look, all of that could prove to be wrong. Only diligent intelligence work is going to find out the truth of it. But if you have to read tea leaves, that would be my guess.

Zack Beauchamp: What's striking to me is it just didn't seem, previously, that ISIS had the capability to plan this type of international attack. Does this tell us something, if it was in fact centrally planned, about ISIS's capabilities that we didn't understand previously?

Will McCants: Yeah. I mean, if this does go back to ISIS Central, it suggests that they were shifting resources toward developing a foreign operation capability. I remember there was an article from a few months ago, reporting from anonymous intelligence sources, saying that they were thinking about this kind of shift, but we didn't see it in their targeting or attack strategy. They may have been developing this capability for quite some time, and it's only now that they are unleashing it.

Even if it's not centrally planned, it's very bad. If they're not even trying to coordinate this kind of stuff, and their affiliates or fan boys can do it on their own, it's quite troubling.

But if the Paris attack was centrally directed, it's even worse. ISIS is a state that has millions of dollars that it can spend on these kinds of operations.

We're not talking about al-Qaeda hiding out in Pakistan. We're talking about an actual government that has money to put behind plots and has very motivated people, many of them with European passports that can carry them out. That's a real problem for the counterterrorism security apparatus if ISIS has indeed shifted its goal or strategy. That's the first thing to determine: Did ISIS Central do this? Did they do all three?

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