By Crispian Balmer
BEIRUT (Reuters) - Syrian President Bashar al-Assad cannot regain full control of his battered country and his rebel foes are not strong enough to overthrow him, dooming Syria to months or even years of sectarian civil war.
Bolstered by his Iranian and Russian backers, Assad has chalked up some military successes in recent weeks, defying his many critics, who have been confidently predicting his imminent downfall since the start of the uprising in March 2011.
But any suggestion his government might secure the total defeat of its disparate opponents shows little understanding of the nature of the war or the multitude of forces involved.
"As things stand, the regime cannot reconquer, it cannot reconcile, it cannot reform and it cannot rebuild," said Peter Harling, a project director at the International Crisis Group.
"But winning is living another day, and if you bring it down to that, (Assad) is," he told Reuters.
As recently as December, Germany's foreign intelligence agency stated openly that Assad's government appeared to be "in its final stages", citing its loss of control over swathes of territory and signs the rebels were co-ordinating better.
Fast forward just five months, and the agency has turned that assessment on its head, a security source in Berlin said.
Germany now believes it is the opposition that faces serious difficulties, hobbled by internal strife and forced into retreat by the arrival of well-trained Lebanese Hezbollah guerrillas, who have gone to war to fight for Assad's survival.
However, a senior official in neighboring Israel, reputed to have some of the best intelligence on its old enemy Syria, dismissed the idea that Assad was staging a remarkable recovery and could once again take full charge of his scarred nation.
"It's a roller coaster, up and down, but over time you see Assad shrinking," said the top official, adding that recent government gains might prove hard to maintain. "It could all change tomorrow," he said.
Recent history shows that most civil wars do not finish quickly, they do not tend to end in negotiated settlements and the longer they continue, the more difficult it is to disarm the militia and unravel the inevitable refugee crises.
The Syrian crisis is now in its third year, with at least 80,000 killed and more than 1.6 million refugees fleeing abroad.
Despite much hand-wringing in the West, the bloodletting looks set to carry on for much longer. According to Barbara Walter, a professor at the University of California, San Diego, civil wars since 1945 have lasted an average 10 years.
Some analysts are starting to draw parallels with the civil war in Lebanon, which dragged on from 1975-1990
"Yes, the Syrian war will last for many years ... And no, Assad will not emerge victorious," said Walter, who has written extensively about civil wars around the world.
On paper, Assad's position looks encouraging for his allies.
The rebels have managed to take only one of Syria's 14 provincial capitals - Raqqa, in the northeast. By contrast, Saddam Hussein lost control of 15 of Iraq's 18 provinces after the 1991 Gulf War but fought back to survive another 12 years.
Assad's forces have also honed their tactics, with irregular militias trained in urban warfare joining the fray while the army concentrates its considerable firepower on key areas.
"Before, a rocket used to fall every 10 minutes. Their new strategy is to hit us with 10 rockets every 15 seconds. We can't figure out how to move fast enough to react," said a rebel contact in the battered city of Homs, declining to be named.
Another big boost has come from Hezbollah, which has openly committed its powerful forces to fight the poorly armed rebels.
"Hezbollah's presence has made a big difference. They are a real force. Army soldiers can defect. Hezbollah fights until the last breath," said an anti-Assad activist called Ahmed, who used to work with a rebel unit in Idlib, northwestern Syria.
Underscoring the rebel problems, Ahmed recently quit his unit, upset by constant infighting within opposition ranks.
Despite the improvement in the outlook for Assad, the dynamics of civil war make it hard to imagine he can triumph.
"I do not recall one civil war that has lasted for more than two years and that has ended with a complete restoration of control by the central government," said Jonathan Eyal, head of international studies at the Royal United Services Institute.
New patterns of power are emerging as Syria is torn apart, state institutions fray and the economy is devastated. The huge influx of arms means it may take decades to restore order.
The war's regional, ethnic and sectarian nature is a further element that looks likely to fuel the fighting, with largely Sunni Muslim states such as Turkey, Saudi Arabia and Qatar lined up behind the rebels, while Shi'ite Iran backs Assad.
"Even if the opposition was crushed, it would not be in the interests of most Arab states to abandon them because they would want to have an instrument to keep putting pressure on Assad and Iran," said Eyal.
Many other jarring interests are at play, making it difficult to see how any diplomatic solution could be found - despite U.S. and Russian efforts to hold an international peace conference in Geneva in the coming weeks.
The initial popular uprising has morphed into a many-layered conflict, with Syrian religious minorities pitted against the Sunni majority, Sunni jihadis at odds with more moderate Sunni Islamist rebels, quasi-Cold War tensions between Moscow and Washington, and Israeli concerns over its own security.
In the absence of decisive foreign intervention on behalf of the rebels - for which the West has shown little appetite - Assad's opponents point to two possible triggers for his downfall: a complete economic meltdown or else a coup.
But neither event would necessarily end the fighting.
Perhaps the best the world can hope for in the near future is a reduction in the intensity of the conflict, which U.S. academic James Fearon says has proved one of the most intense civil wars in the last 60 years in terms of numbers killed.
"As a practical matter it is hard to sustain this level of violence on both sides for a long time," said Fearon, professor of political science at Stanford University.
"However, even if the intensity of violence reduces a lot, the likelihood of years of continued lower-level but still serious violence in Syria must be judged to be pretty high."
(Additional reporting by Erika Solomon and Dominic Evans in Beirut and Sabine Siebold in Berlin)