Twelve days after the attacks, and Paris can breathe again. Signs of the French capital's transformation into a war zone — the bodies draped in white sheets, the blood-soaked streets, the night raids, the curfews, the suburban caches of AK-47s, the evacuations of world-famous landmarks, and the earnest appeals of Parisian taxi drivers to "Have courage!" — have now dissipated.
But around the Élysée Palace, the official residence of the French president, the talk is very much still of war, a word that appeared in the public discourse on the very day of the attacks.
In a speech to a joint session of parliament soon after the coordinated attacks in Paris on November 13, which left at least 130 dead and hundreds more injured, President François Hollande declared the country to be "at war," and vowed to be "merciless" with the Islamic State.
Imposing a nationwide state of emergency, Hollande promised to reform France's constitution, giving his government more sweeping powers to fight terrorism, and to put the country's economy on a war footing, privileging short-term military expenditures over the European Union's budget mandates.
On November 18, he dispatched the Charles de Gaulle aircraft carrier to the eastern Mediterranean, where it is reportedly carrying out air strikes against Islamic State targets.
The bookish Hollande, known at home as a "marshmallow" for his perceived soft and wobbly demeanor, also adopted a warlike language.
In the days following the attacks, French officials built on this language — imagining "a large coalition" of Western powers that could "decisively" bring IS insurgents to their knees. France must "galvanize the international community as a whole to vanquish our shared enemy," said François Delattre, France's ambassador to the United Nations.
On Tuesday, Hollande traveled to Washington, to continue his diplomatic offensive. A few hours after speaking to President Barack Obama, he turned his plane to Moscow, for more of the same with Vladimir Putin. On Monday, the president had met with British Prime Minister David Cameron, who said he would push his parliament to approve military action in Syria.
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So are we all at war? And if so, against whom? And on whose team, and to what end, and with what legal foundation?
The Paris attacks have already inspired a debate about whether France's allies will necessarily be drawn into a global campaign against IS — and how a less-than-unified global coalition might conduct "war" collaboratively against a non-state enemy that relies on irregular warfare and asymmetric assaults that are difficult to anticipate.
A number of politicians and legal scholars of varying stripes have argued that the Paris precedent will make it easier to fight IS legally. (The viability of such a war remains hotly contested — especially given that Western nations are reluctant to put boots on Syrian ground.)
These experts' anticipated roads to war, however, diverge. Some argue that the NATO alliance will use the attacks in Paris to invoke Article 5 of its 1949 Washington Treaty, and thus initiate a collective military campaign.
Others counter that NATO member states like France and the US are already carrying out piecemeal assaults against IS on their own — and argue simply that the Paris attacks will put these strikes on less sketchy legal footing.
Legal critics have blasted Obama for failing to obtain Congressional support for his strikes on IS in Syria, though Washington insists that the actions are covered by the broader 2001 Authorization for Use of Military Force, passed after 9/11. In Britain, Prime Minister David Cameron has pledged aid to France and is pushing for his own strikes in Syria — but has yet to win a parliamentary vote on the matter.
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Thus far, France has not asked NATO to organize an alliance-wide response, as many predicted would happen in the days after the attacks.
This process would begin with Paris demanding a "consultation" under the Washington Treaty's Article 4. The last Article 4 consultation took place in July at Turkey's request, following IS attacks there.
At a consultation, NATO delegates would determine whether the Paris attacks meet the criteria of another part of the Treaty, Article 5, which famously states, "an attack against one ally is considered an attack against all allies." If Article 5 were invoked, NATO could lead a "collective defense," summoning up to 3 million armed troops, and 25,000 military aircraft — backed by 28 countries representing more than half of the world's GDP.
Already, former NATO chief Anders Fogh Rasmussen has judged that "the attacks on Paris qualify for an invocation of Article 5." Admiral James Stavridis, a former NATO Supreme Allied Commander, has embarked on a whirlwind tour of American media outlets to argue that France could, and should, demand a full-on NATO war.
"There is a time for soft power and playing the long game in the Middle East," Stavridis wrote in Foreign Policy, "but there is also a time for the ruthless application of hard power."
Yet Article 5 is not a panacea. Its language calls for member-states to "assist the party or parties so attacked by taking forthwith… such action as it deems necessary, including the use of armed force."
But "necessary" is undefined — and does not necessarily require military might. It could include, for instance, intelligence sharing, or law enforcement co-operation across European Union borders, rather than shoulder-to-shoulder troops in Raqqa, the de facto capital of the Islamic State self-defined "caliphate."
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Article 5 has only been invoked once in history, after the 9/11 attacks. That invocation marked an enormous departure from the intended purpose of the article, as conceived half a century earlier.
Then, in 1949, NATO members had the Soviets in mind. Its proponents assumed that if Article 5 were ever invoked, it would be because a belligerent Soviet Union attacked Europe in a blitzkrieg-style assault, and America would be summoned to save the day.
Rather, in 2001, it was the Europeans who were called to Washington's side. And a precedent was set: that Article 5 "armed attacks" need, yes, to be directed by foreign enemies — but that those enemies could be non-state and irregular actors.
In the wake of the Paris attacks, some experts argue that Article 5 requires a retooling, to respond to a post-Cold War security environment. Already, since 9/11, NATO has built new command structures, led missions outside Alliance territory, and developed new counter-terrorism capabilities.
But, "if NATO wants to maintain its relevance, it has to do something," said Sebastian Gorka, of the Atlantic Council's Strategic Advisers Group. It "perhaps needs to write a new strategic concept that embraces unconventional threats and irregular warfare as the meat and potatoes of future NATO missions."
Those unconventional threats might include cyber-ops, lone-wolf terrorists, energy and infrastructure threats, and information warfare — challenges ill suited to a response from NATO's prized "mobile and deployable" forces, and for which proportional responses are difficult to devise.
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In fact, despite their martial talk, France and its allies might prefer for NATO not to take the lead in a fight against IS. A loose coalition of states is already striking against insurgents in Syria — and is, effectively, already at war. France has been bombing IS targets in Syria since September.
NATO involvement would require a level of member-state consensus that could slow things down. It would almost certainly complicate relations with Russia, which has its own, divergent objectives in Syria — and which, this week, is busy lashing out against Turkey, following the shooting down of a Russian warplane by Turkish forces on Tuesday.
Historian Stanley Sloan has argued, in addition, that France "remains protective of its national sovereignty" and would be loath to relinquish any control to NATO's Supreme Allied Commander (an American). Hollande might also find it politically undesirable to cede military authority, keen as he is to shore up his military credentials in the lead-up to regional elections in December.
Historically, France has had a strained relationship with NATO. It pulled out of the military alliance in 1966, only rejoining in 2009.
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In the meantime, France has taken smaller steps towards a multi-national response, within the European Union. On November 16, Hollande requested, and EU member states unanimously invoked, the EU Lisbon Treaty's little-known Clause 42.7, which states: "If a member state is the victim of armed aggression on its territory, the other member states shall have towards it an obligation of aid and assistance by all the means in their power." The mutual defense provision was inserted after a terrorist attack in Madrid in 2004.
But this was the first time that the clause was ever used. In fact, some EU officials told reporters that, until Hollande referenced 42.7, they had never heard of it.
Clause 42.7 may push EU states to implement new counterterrorism measures. It could also lead them to give France military assistance abroad — say, in the form of personnel backup in the Sahel region, the Central African Republic, or Lebanon, which would in turn let France focus its resources on IS. "France can't do everything," bemoaned French Defense Minister Jean-Yves Le Drian, last week.
Appealing to the EU, as opposed to NATO, is perceived as a less belligerent move, in part because the Union isn't a military alliance. Clause 42.7 can also be implemented more speedily, since it relies on state-to-state agreements rather than formal, Union-wide procedures.
According to EU foreign policy chief Federica Mogherini, several EU states "have already announced offers or support through material assistance as well as to enhance support in other theaters."
But as is the case with NATO's Article 5, the Lisbon Treaty's "aid and assistance" does not necessarily mean troops. Already, the Czech Republic's foreign minister has said that he does "not expect any contribution as far as troops are concerned for France because it is a big powerful country and has its own capacities."
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Some critics argue that any sort of unified military action against IS is unlikely — and that, instead, individual nations will seek to individually justify their own "war" in Syria.
This process could be helped along by a UN Security Council resolution, passed on Friday, which urges countries to "take all necessary measures" to destroy IS and its "safe havens" in Iraq and Syria. The resolution confirms that IS an ongoing terrorist threat.
Yet Resolution 2249 fell short of invoking Chapter 7 of the UN charter, which is used to authorize military action, perhaps because Russia and/or China, which have veto power in the Security Council, opposed it. What exactly the resolution allows, or should inspire, is vague.
In the absence of a Chapter 7 invocation, nation-states still need state their own individual cases for why their strikes against IS are necessary. They may plead self-defense, for example.
But the "self-defense" argument has long been contentious. Both the US and UK have argued self-defense, though neither have been attacked by IS on their home turf.
This is critical, from a legal perspective. "It is not permissible in international law to use force in retaliation — to say 'You struck us, so now we will strike you,'" said Professor Marc Weller, an international legal scholar at Cambridge University. "It would only be permissible to use force if there is credible evidence that a foreign agent is going to mount the next armed attack and that was confirmed by the Security Council."
The Security Council resolution would not retroactively legalize a previously illegal military strike.
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This is, of course, still an academic discussion. A bona fide "war" against IS would almost certainly require ground troops, and no NATO or EU state has plans to commit them as yet.
On November 16, US President Obama affirmed that it would be a "mistake" to launch a full-scale ground operation in Syria. Memories of failure in Afghanistan and Iraq loom large. "Not because our military could not march into… Raqqa and temporarily clear out ISIL," he said, "but because we would see a repetition of what we've seen before." The US has opted instead to support Kurdish forces and conduct air strikes on Syrian targets.
Meanwhile, back in Paris, some have criticized the French government for its warrior rhetoric.
After all, a handful of this month's attackers were French nationals. And so, if France is going to be at "war" with IS, it must also brace itself for civil struggle.
Follow Katie Engelhart on Twitter: @katieengelhart.