A weathered Middle East truism holds that, while there can be no all-out Arab-Israeli war without Egypt, there can be no long-term peace without Syria. Poor and militarily feeble, Syria has used its location as a geopolitical hub and its nimble, ruthless politics to make itself indispensable to the regional order.
But as a two-month-old uprising against the regime of President Bashar Al Assad refuses to be suppressed, Syria risks losing that position as a linchpin, perhaps enough to alter the Middle East's balance of power.
"When something has been in the icebox for 40 years, there is no telling how it will look when it melts," says a human-rights activist who covers Syria, referring to the decades of dictatorship under Al Assad and his father, Hafez, an air-force commander who seized power in 1970. The prospect of prolonged unrest, outright anarchy or sudden regime change confronts all Syria's neighbours, as well as allies such as Iran, Hezbollah, and various Palestinian factions, including Hamas, with a conundrum.
Most of them would rather Al Assad stayed. Even the Israelis, despite seeing Syria as their most diehard Arab foe, know that the Al Assads have kept their mutual border quiet. Iraq, now shakily ruled by its Shiite majority after ugly years of sectarian war, fears what may happen if Syria's Sunni majority, three-quarters of the population, seized power after decades of domination by Al Assad's Alawites, an offshoot of Shiite Islam numbering a tenth of Syria's people.
Turkey, which has cultivated close ties to Al Assad as part of its ‘zero problems' policy, also fears chaos on its longest border and the empowerment of Syria's long-oppressed Kurdish minority.
Polarised as always, the neighbouring Lebanese differ starkly over the predicament faced by Syria, where the regime has long exercised undue influence on Lebanon's own messy sectarian politics.
Hezbollah, seeing its physical link to its Iranian mother-ship threatened, could drop its pretences that it respects Lebanese democracy, in which it has played a largely behind-the-scenes role. "Hezbollah will not take this lying down," warns a politics professor in Beirut, contemplating the Al Assads' possible downfall. "They will make a coup and take over the system."
But even among his allies the brutal tactics used by Al Assad, including mass arrests and the deployment of tanks, artillery and snipers against unarmed crowds, have muted support for his regime. The Al Assads have long-drawn legitimacy from their dogged support of Palestinian rights.
Yet the sight of Palestinian protesters storming border fences along the occupied Golan Heights, as they did on May 15, was widely dismissed in the Arab press as a ploy to divert attention from Syria's own troubles. For the Israelis it suggested that a flailing Al Assad regime might be worse for them than an untested new one.
On the ground in Syria the protesters' failure so far to disrupt ordinary life much in the two biggest cities, Damascus and Aleppo, helps the regime to portray the unrest as small and scattered incidents provoked by foreign agitators.
Syrian officials say government forces have won the upper hand in the peripheral zones where rebellion has spread, insisting it is now a matter of time before the protests fade.
Most commentators think the regime is in no imminent danger of collapse. In Egypt and Tunisia more professional armies refused to open fire to save their beleaguered presidents after the collapse of the police. But Syria's army is designed to protect the regime.
Syria's opposition is diffuse and still leaderless. Over the years the regime has co-opted much of the urban Sunni middle class and convinced other groups, such as the Christian minority of some 10 per cent, that without Al Assad, Syria may descend into civil war in the manner of Iraq or Lebanon.
Sectarian hatred, initially played up by the regime to rally support from other minorities, is becoming a reality. It is not a coincidence that the most persistent revolts and the worst retribution have occurred in Sunni-dominated areas. Sporadic attacks on security forces, of whom the government says 120 have been killed, seem to have specifically targeted Alawite officers.
"We're in for at least six months more of this," reckons a Damascus businessman who has prospered under Al Assad's rule. "After that we'll have a weakened Bashar limping along or the generals will decide that the Al Assads are a liability."