BEIRUT – The expected fall of Aleppo to the regime of Syrian president Bashar al-Assad could prove a decisive moment in Syria’s grueling civil war, granting potential momentum for the Syrian army and its multinational allies to roll back rebel forces from other areas of the war-torn country.

The Syrian army has been dogged by manpower shortages from early on in the war due to casualties, defections and desertions. More than once, those have threatened doom for the Assad regime. But the deployment of foreign, Iran-supported Shiite paramilitaries, the creation of numerous loyalist militias and, in the past year, the arrival of Russian firepower may have finally tipped the military balance in Assad’s favor.

Regaining the whole country – a publicly stated goal of Assad’s – may seem overly ambitious at this stage. But the declining levels of foreign support for the beleaguered rebel groups over the past year and the momentum created by the imminent fall of Aleppo place the regime in a potentially advantageous position to recapture the rest of the western half of the country, sometimes dubbed the “essential Syria,” which holds the bulk of the population and urban areas.

“It is a turning point, but to what remains unclear,” says Andrew Tabler, a Syria expert at the Washington Institute for Near East Policy. “But Aleppo’s fall is important in the regime’s attempt to consolidate its lines of control and ‘essential Syria.’”

Decisive Gains

Regime forces, backed by artillery bombardments and Syrian and Russian airstrikes, have made decisive gains in Aleppo since the weekend, overrunning rebel-held neighborhoods in the northeast part of the city. The United Nations on Tuesday said that some 16,000 people have fled the fighting in recent days. Some have crossed into the government-controlled western half of the city and others to a Kurdish-held area to the north. The rebels are now holed up in the southeast quarter of the city, but conditions are desperate, with food supplies running critically low and no functioning hospitals left.

“The parties to the conflict in Syria have shown time and again that they are willing to take any action to secure military advantage even if it means killing, maiming or starving civilians into submission in the process,” said Stephen O’Brien, the U.N. humanitarian chief and relief coordinator, in a statement Tuesday.

While the focus has been on Aleppo, the regime’s brutal policies in rebel-held areas are deployed in other areas of the country, as well. That often leads to evacuation deals in which rebel fighters are allowed safe passage to other opposition enclaves. The U.N. said that some 700,000 people are living under siege, mainly in the eastern and western Ghouta areas around Damascus.

Last week, rebel forces in Khan al-Shih, which sits on the vital highway linking Damascus to Daraa in southern Syria, agreed to surrender their heavy weapons and relocate to Idlib province, which has been under rebel control since early 2015.

Not Enough Fighters

Since the conflict in Syria began in 2011, the Assad regime has been plagued by manpower shortages in its military forces. At the outset of the conflict, the Syrian military had an on-paper strength of more than 300,000 personnel (including air force and navy), although its actual numbers were believed to be considerably less. But casualties, desertions, defections and war fatigue took a heavy toll. New ad hoc units were cobbled together, and the government forcibly recruited young men into the army’s ranks. But it was not enough.

By early 2013, when Assad was close to losing Damascus, Lebanon’s Shiite Hezbollah organization began deploying in greater numbers, helping beat back the armed opposition in the capital and securing tranches of territory adjacent to the Lebanese border. Thousands of Shiite volunteers from Iraq traveled to Syria and were mobilized into militias under the guidance of the Iranian Revolutionary Guards Corps (IRGC). The IRGC also helped train the National Defense Force, a Syrian loyalist militia. Other local militias were established and paid for by prominent businessmen close to the regime. Additional Shiite fighters from Afghanistan and Pakistan arrived in Syria and were marshaled into the Fatimiyoun and Zeinabiyoun brigades respectively, also under IRGC control.

Still, in early 2015, Assad began to lose significant swathes of territory in the north when a coalition of rebel forces seized much of Idlib province and was poised to sweep south toward the central city of Hama and west toward Latakia on the Mediterranean coast.

But by September Russia had waded into the Syria war, deploying aircraft to an air base near Latakia in what Moscow said was an operation against the extremist Islamic State and other radical groups. But Russian firepower, which was augmented by Spetsnaz special forces and motorized rifle brigades and this month by a naval carrier group off the Syrian coast, has mainly been used to assist government forces to beat back the rebels.

The imminent fall of Aleppo suggests that Russian intervention has been a game-changer for Assad. And with rebels losing ground around Damascus and the opposition effectively dormant in southern Syria, the regime will have more men to deploy to crucial areas in the north.

“I think the insurgency will be under control soon,” says Faysal Itani, a senior fellow at the Atlantic Council’s Rafik Hariri Center for the Middle East. He added that Assad still lacked the manpower to regain and garrison the entire country, but “the situation in which rebels take and hold large swathes of territory will be finished.”

The rebel forces still have plenty of fight left in them, but the future is looking uncertain. The next administration in Washington appears more interested in improving ties with Moscow and seems to share the current administration’s reluctance to help the Syrian opposition unseat Assad. The Assad regime so far has shown little appetite for a serious negotiated settlement, which may not change now that it has the upper hand militarily.

That does not bode well for the opposition’s long-term prospects.

“They [the rebels] are under huge pressure,” says Yezid Sayegh, senior associate at the Carnegie Middle East Center in Beirut. “The Syrian opposition is now going to face a very difficult task of being able to assess what they can now hold out for and when to accept terms. That’s going to be really hard because it’s not an opposition that’s very cohesive.”

This article was originally published by the Christian Science Monitor and is reprinted here with permission.