Olivier Roy writes: As President François Hollande of France has declared, the country is at war with the Islamic State. France considers the Islamist group, also known as ISIS, to be its greatest enemy today. It fights it on the front lines alongside the Americans in the Middle East, and as the sole Western nation in the Sahel. It has committed to this battle, first started in Mali in 2013, a share of its armed forces much greater than has the United States.

On Friday night, France paid the price for this. Messages expressing solidarity have since poured in from all over the Western world. Yet France stands oddly alone: Until now, no other state has treated ISIS as the greatest strategic threat to the world today.

The main actors in the Middle East deem other enemies to be more important. Bashar al-Assad’s main adversary is the Syrian opposition — now also the main target of Russia, which supports him. Mr. Assad would indeed benefit from there being nothing between him and ISIS: That would allow him to cast himself as the last bastion against Islamist terrorism, and to reclaim in the eyes of the West the legitimacy he lost by so violently repressing his own people.

The Turkish government is very clear: Its main enemy is Kurdish separatism. And a victory of Syrian Kurds over ISIS might allow the Kurdistan Workers’ Party, or P.K.K., to gain a sanctuary, and resume its armed struggle against Turkey. [Continue reading…]