The morning after Obama promised to “degrade and ultimately destroy” Isis, Lebanon woke up to news of more fatal clashes with jihadists on its fraying borders. In Beirut’s glittering Downtown district, workers were morose. Taxi driver Imad used to make a good living ferrying expatriates between shops, hotels and restaurants. “Now there are no clients,” he complained. “The tourists are afraid to come, between Hezbollah fighting and these extremists cutting off heads.”

Six months ago anyone could drive through this exclusive part of town, framed by the elegant Lebanese parliament and the blue Mediterranean. Now army checkpoints and tanks block its wide boulevards. Heavily armed security squads guard its embassies and political centres, including the house of dynastic former prime minister Saad Hariri. It was Saad’s father, the murdered Rafiq Hariri, who conjured Beirut’s rebirth from the rubble of a 15-year civil war. He believed his fractured country could be reconstructed as a modern engine, its sectarian parts spinning together on a prosperous journey greased by capitalism. Today, Hariri’s vision dominates Beirut’s skyline, a phoenix risen in a blaze of glass towers, marble façades and expensive souks.

But Lebanon’s engine is being derailed, along with its fragile equilibrium. Last month, the Lebanese Armed Forces (LAF) was dispatched to Arsal, a town on the Syrian border choked with refugees, dust and sectarian in-fighting where Isis and Salafist rivals Jabhat Al-Nusra had seized control. One hundred people died in the battle to retake Arsal and 29 Lebanese soldiers were captured. Two have since been beheaded. Isis is threatening more deaths to follow. […]