With the Syrian crisis entering its fifth year, a months-long campaign by the largest antigovernment militia in the south to march on Damascus and turn the tide of the war has become a bitter fight for its very survival.

The Free Syrian Army (FSA), once seen as a natural US ally for toppling the regime of President Bashar al-Assad, is locked in a showdown with an alliance of government forces, Lebanese Hezbollah fighters, and Iranian-commanded Shiite militias.

The battle is being waged in an area south of Damascus and east of the Israeli-held Golan Heights, a theater that had been the quietest in the Syrian conflict. The stakes are high for all sides, ranging from the Assad regime’s stable hold on the capital to the viability of the FSA at a time when the US is struggling to find pro-Western rebels in Syria to arm and train – and keep them from joining jihadist factions that increasingly have the upper hand in the war.

For Iran, looking beyond the fate of its ally, Assad, the battle has implications for its strategic aspirations on Israel’s northeast frontier.

For four months, the FSA had been mounting a steady offensive to recapture the revolution’s momentum. Overcoming dwindling supplies and limited arms, the rebel force of 12 brigades comprising some 20,000 FSA fighters had battled inch by inch to capture the main highway linking the southern city of Daraa to Damascus.

The campaign’s goals were both strategic and symbolic. Control of the Daraa-Damascus highway would allow the FSA to rapidly funnel arms, supplies, and troops from the Jordanian-Syrian border to Damascus and to nearby suburbs in eastern Ghouta district, where another force of 12,000 FSA fighters is fighting on despite a blockade imposed by Syrian forces.

In addition to breaking the blockade and allowing FSA forces unfettered movement from southern to central Syria, the capture of the highway would provide FSA forces the access to launch a wider offensive within Damascus itself.

Rebel commanders say the sight of FSA brigades operating in the heart of Damascus would rekindle hope among a Syrian public that is both fatigued by war and disillusioned with an opposition that has failed to fulfill its promises.

“For us, the path to saving the revolution, saving the Free Syrian Army and the Syrian people is clear – it runs from Daraa to Damascus,” says Assad Zoubi, commander of FSA forces in the southern region and a former air force major general.

“If we can arrive at Damascus, the whole conflict would change. It is our last best hope.”

Militias hit back

Throughout most of the campaign, from November through early February, rebel forces including the FSA’s First Army and Yarmouk brigades were met with resistance by only a few thousand regime troops from the 7th infantry division, with Damascus reportedly relying on its airpower to contain the ever-advancing FSA forces.

By Feb. 8, FSA forces had pushed all their way to the village of Kanaker and prepared for a siege of the town of Zakiya, a feat which would have placed the rebel forces 20 kilometers (about 12 miles) from the outskirts of Damascus proper – well within the range of the rebel army’s surface-to-surface missiles.

Yet before the offensive could be launched, the tide quickly turned, with the government that day announcing a counter-offensive in the south, the so-called “battle of determination.”

The government quickly amassed an estimated 8,000-strong force of foreign Shiite fighters south of Damascus, including Hezbollah, Iraqi, Afghani, and Iranian Revolutionary Guard Corps (IRGC) fighters, according to rebel, Hezbollah, and pro-regime sources.

The campaign’s goals went beyond simply driving rebel forces from Damascus’s gates to include pushing the FSA from the south, recapturing the northern borders of the Golan Heights, and dismantling the rebel forces once and for all.

‘Triangle of death’

The focus of the ongoing fever-pitched battles has been a 20-kilometer-wide and 90-kilometer long strip of southwest Syria, stretching from Damascus south along the Golan Heights and encompassing the bulk of southern rebel strongholds.

The Shiite militias, backed by Syrian airpower, have focused their efforts particularly on a small, vital swathe of territory between Daraa in the south, Quneitra and the Golan to the west, and Damascus to the north – what rebel fighters have now dubbed the “triangle of death.”

If the regime succeeds in quarantining the strongholds in the “triangle,” it would cut off vital supply lines for FSA forces, blocking the flow of fighters and arms from the Jordanian border and leaving no room for the Free Syrian Army in the south.

At first, the FSA took a beating from the better-armed Shiite militias, losing seven key villages and towns on the edge of the Damascus countryside. But snow in mid-February slowed the offensive and allowed rebel forces to regroup and push again northwards, temporarily recapturing lost towns.

Rebel forces are reportedly now again on the defensive as regime sources push south toward Quneitra at the edge of the Golan Heights.

“Iran and Hezbollah are driving this campaign – this is no longer a war between the Syrian people and the regime,” says Abdul Hadi Sarra, FSA commander and former air force general.

“They want to make sure that if and when Assad falls, their forces and interests remain intact – particularly the Golan Heights.”

Guerrilla warfare

In recent days, the battle has reportedly stalled into a bloody deadlock near the village of Deir al Maker 20 miles south of Damascus, with either side advancing a few hundred meters per day.

“Every time we try to take a centimeter, they try and take back a meter. Every time they take a hill we try to take two,” said Abu Kamel al Jolani, FSA commander fighting in the southern theater north of Daraa.

“We are fighting a war over meters.”

The conflict has been bloody for both sides. The FSA reports an average of 10 casualties per day, or 300 since the counter-offensive began. Meanwhile, rebel forces claim to have killed more than 400 Shiite militia fighters, including 300 in a single-day offensive in Deir Maker and Himreet south of Damascus.

The Syrian government has so far refused to disclose the number of casualties in the southern theatre.

Despite the losses, the FSA has claimed several “moral victories,” reportedly killing key Shiite militia leaders, including Hezbollah fighters and at least two IRGC officers.

For FSA, victory is survival

But for rebel forces now facing this broad coalition, it’s become a fight for mere survival.

Rebel forces fear Damascus will redeploy thousands more Shiite militia fighters to the south. As spring brings better weather, the flying conditions for the Syrian air force are also improving. On Tuesday regime warplanes carried out 22 sorties.

The loss of the south would rob the Free Syrian Army of its last remaining base of operations within Syrian territory.

The FSA – which has long suffered internal divisions and lack of leadership – would “cease to exist” should it fall in the south, FSA commanders say.

The dissolution of the FSA would leave more than 60,000 armed rebel fighters without a command or structure – a potential recruitment boon for hardline jihadist militias such as Al Qaeda-aligned Jabhat al Nusra, which has absorbed thousands of FSA defectors in recent months.

The departure of the FSA would also allow space for the Islamic State, which until now has had a limited presence of 400 fighters in the south, to threaten the Jordanian border and the Golan Heights.

The defeat would also deal a blow to Sunni Arab states Saudi Arabia, Jordan, Qatar, and the UAE, which have either funded, armed for facilitated the transport of fighters to support Sunni militias in Syria.

“It would be not only a defeat for the FSA,” says Andrew Tabler, a Syria expert at the Washington Institute for Near East Policy, “but another setback for their regional Sunni backers, as well as Israel.”

“We all know this is not a battle for the south,” says Mr. Zoubi, the southern FSA commander.

Get the Monitor Stories you care about delivered to your inbox. By signing up, you agree to our Privacy Policy

“This is the battle for Syria.”

Correspondent Nicholas Blanford contributed reporting from Beirut.