“WE lurch from crisis to crisis, with superficial calms in between. But the crises are coming closer and could soon merge into a single, all-consuming crisis.” So warned Muhammad Shatah last month. Two weeks later, on December 27th, Lebanon’s 62-year-old former finance minister and ambassador to Washington was dead, killed along with seven others when a remote-controlled bomb punched a fireball into his passing car.

Around the site of the blast in Beirut’s central business district and across other posh parts of Lebanon’s capital, construction cranes loom amid a ceaseless racket of pile-drivers. Such relentless industry testifies to Lebanon’s resilience, despite the proximity of the bloodbath across the Syrian border, barely an hour’s drive from Beirut. More than 1m Syrians have already fled to safety here; they may now make up a quarter of Lebanon’s population, previously 4m. Syrians now man the building crews, just as Syrian flight capital and war profits largely keep housing prices high.

But as Mr Shatah suggested and his death underscored (his funeral is pictured above), the flimsy barriers that have spared this tiny country from a far greater deluge of woes grow weaker by the day. Papered over for two decades, the cracks from Lebanon’s own brutal civil war of 1975 to 1990 have widened and spread. Syria is partly the cause. As its popular uprising has descended into a vicious slugging match between increasingly chauvinistic sects, tensions have grown among Lebanon’s own complex religious mix—around a third of its people are Sunni Muslim, a third Shia and a third Christian.

Lebanon’s Sunnis broadly share the rage of Syria’s battered Sunni majority; its Shias share the fears of the defiant minorities that form the core of support for Bashar Assad’s regime. The regional rivalries, chiefly between Shia Iran and arch-Sunni Saudi Arabia, that have made Syria a proxy war are also reflected in Lebanon.

For three decades Iran’s Revolutionary Guard has nurtured and funded Hizbullah, Lebanon’s powerful Shia party-cum-militia. Disciplined and ruthless, Hizbullah has in effect used Shia unity to gain a stronghold over much of Lebanon’s feeble state, and a veto over policy. Alarmed by military setbacks to Mr Assad’s regime earlier last year, the party belatedly plunged into Syria’s fray. Its fighters have helped relieve Damascus, the Syrian capital, but at a painful cost. Perhaps 500 Hizbullah combatants have died in the fighting, say independent analysts, more than during the war it fought with Israel in 2006.

Politically fractious and geographically dispersed, Lebanon’s Sunnis have no similarly dominant militia. And Syria’s strife has sapped the influence of traditionally moderate Sunni leaders. With Lebanon’s current government unable to control arms smuggling, radical Sunni gangs have proliferated, many with links to Syrian rebels. Lebanon’s Christians, meanwhile, remain split, too. Some back a Hizbullah-led, pro-Syrian political front known as March 8th. Others, along with much of Lebanon’s diverse but militarily impotent political centre, back the rival, pro-Western, Saudi-supported March 14th group, of which Mr Shatah was a figurehead.

For the first part of Syria’s 33-month-long war, the stark polarisation in Lebanon was contained within its shaky, nominally democratic politics, bound by rules that allot each sect a proportion of government posts and powers. Last March the elected prime minister, by tradition a Sunni, resigned in protest against Hizbullah obstruction. After much wrangling the almost evenly split parliament designated a new prime minister, but hostility between the March 8th and March 14th groups has so far prevented him forming a cabinet, leaving his predecessor, Najib Mikati, to run a weakened caretaker government.

But Lebanon’s rivalries have begun leaking out of politics and into violence. In 2013 nearly 100 Lebanese died in bombings that targeted—variously and at a growing rate of frequency—mosques in the largely Sunni city of Tripoli, Shia-dominated suburbs of Beirut and, in November, Iran’s embassy. Assassins struck down a senior Hizbullah official as well as Mr Shatah, whose death follows a chain of killings that have punctured the March 14th leadership, starting with a bomb in February 2005 that killed the faction’s founder, Rafik Hariri, who had served five stints as Lebanon’s prime minister.

Sunni radical groups have claimed responsibility for the attacks on Hizbullah, but the Shia militia and its allies still pin the blame broadly on March 14th, the Sunnis’ most popular movement. This group’s supporters, while not excluding direct Syrian involvement, are increasingly open in charging Hizbullah with a campaign of terror against its foes. Mourners at Mr Shatah’s funeral chanted insults against Hizbullah, as one orator vowed to liberate Lebanon from “occupation by illegal arms”, a reference to complaints that Hizbullah poses as a resistance force against Israel while in reality using its armed might to blackmail weaker political rivals.

Held in check so far by shared memories of Lebanon’s descent into civil war 38 years ago, such tensions may yet explode. A long-delayed trial of four fugitive Hizbullah men charged with killing Hariri is due to start in an international court in The Hague on January 16th. And unless Lebanon’s parliament, which has not met in months, chooses a new president by the spring, the country will enter a dangerous constitutional vacuum. “We face having no legitimate government at a time of the greatest challenge to the Lebanese state,” says Yezid Sayigh of the Carnegie Middle East Centre in Beirut, a think-tank. “What we have now can’t be called a civil war, and it may not become one. But it is a shadow war.”