...The Middle Eastern country took its current shape as a French mandate after being chiseled out of the Ottoman Empire after World War I, as did neighboring Lebanon, and French is spoken by many in both countries. France has particularly close ties to Lebanon and wants to prevent it from being sucked further into Syria’s chaos.

The ties to the region also make Syria a particularly attractive place for homegrown French extremists. French Interior Minister Manuel Valls said this month that about 110 citizens or residents of France have joined up with jihadist fighters in Syria — about half the total number from European Union countries. French authorities fear they will return home to carry out terrorism.

Also, fear of chemical weapons runs deep in France, which is why France has hardened its line since the Aug. 21 attack in which the U.S. and some allies believe Assad’s regime used sarin gas against Syrian citizens. Many French people have ancestors who faced mustard gas in World War I, as chemical weapons scarred public consciousness for the first time....