If any good is to emerge from the worst terrorist-inspired attack in French history, it will be that it finally forced world leaders to acknowledge that the threat posed by Islamic State (Isil) can no longer be ignored.
When French President Francois Hollande denounced the terror attacks on Paris that have so far claimed 129 lives as an "act of war", he was also reflecting the view held by Isil since it declared the creation of its self-styled Caliphate amid the ruins of northern Iraq and Syria: that is committed to an existential struggle to destroy Western infidels.
Yet, so long as Isil confined its murderous activities to the Middle East, the consensus in the West has been that, rather than getting involved in another costly military intervention, containment was the best option. Local, pro-western militias such as the Kurds and more moderate elements within the Syrian opposition were charged with reversing Isil's gains on the ground, with the US-led coalition limiting its involvement to air strikes.
This strategy may even have worked had Isil confined its activities to the Caliphate. But, from its inception, Isil's leadership has made it clear that its ambitions lie far beyond Arabian shores. It aims to spread its extreme ideology throughout the four corners of the globe, with specific focus on Europe, referred to in Isil literature as "Rome", the great power that was in decline when the first Islamic caliphs rose to prominence.
Thus the thousands of foreign jihadists who have flocked to join Isil in recent years have not travelled just to fight on the battlefield. Many have undergone intensive training on the understanding that they would return home and bring holy war to the streets of their native countries. Now the brutal effects of this policy are being felt throughout the world. Russia yesterday offered a $50 million reward after its intelligence officials confirmed a bomb brought down the jet that crashed in Sinai last month killing all 224 people on board.
In France, meanwhile, investigators are intensifying efforts to find out how Abdelhamid Abaaoud, the alleged Belgian-born mastermind behind the Paris attacks, succeeded in coordinating his assault on the French capital.
Add to these lingering suspicions that Isil was behind the attack at the Tunisian resort of Sousse in June that claimed 30 British fatalities, as well as other outrages, and it is clear the major powers no longer have the option of keeping their distance.
This change of heart was evident at this week's G20 summit in Turkey, where David Cameron and Barack Obama put to one side their differences with Russian President Vladimir Putin over his meddling in Ukraine to discuss making a concerted effort to destroy Isil. Mr Putin has even ordered the Russian military to support the French naval task force that has been dispatched to Syria.
But just because world leaders have belatedly started talking to each other about making common cause against Isil does not mean they have managed to devise a coherent and effective strategy for ending the conflict.
As matters stand there appear to be more obstacles than opportunities for forging a concerted plan of action. For example, Russia's insistence, together with its ally Iran, on the survival of President Bashar al-Assad's regime in Damascus makes it hard for them to agree with Western allies, such as Turkey and Saudi Arabia, that regard Assad's removal as the sine qua non for their support.
This and the myriad other issues that stand in the way of forming an effective anti-Isil coalition could be accommodated if world leaders summoned the political will to set aside their differences. For example, leaving Assad in power for the interim while Isil is dealt with - an option discussed at the recent Vienna talks - could be one option.
Of equal importance, though, is the need to forge a proper military strategy for countries supporting a new anti-Isil military effort. More than a year after coalition warplanes began bombing Isil positions, there is now a general recognition that Isil will not be defeated by air power alone.
Even Mr Cameron, who still entertains hopes of winning Commons approval for allowing the RAF to extend its bombing operations from Iraq into neighbouring Syria, now recognises the limitations of aerial warfare.
Ground forces of some description will be vital if Isil is to be removed from strongholds such as Raqqa in northern Syria and, as there is little appetite for Western boots on the ground, we will need to work closely with pro-Western proxies, such as the Kurds and moderate Syrian opposition groups.
Serious thought must also be given to what happens after Isil is defeated: the key lesson of the Iraq war is that post-conflict planning is as vital as planning for the conflict itself.
In terms of building an anti-Isil coalition, the first Iraq war might serve as a useful precedent. Then nations set aside their differences to defeat Saddam: perhaps now they can do the same to defeat Isil.