Within the past week entire neighborhoods in the rebel-held enclave of eastern Aleppo have fallen to the Syrian government. In this dense urban terrain, forces loyal to President Bashar al-Assad have advanced at a speed that few had thought possible.

As rebel control over eastern Aleppo crumbles, the Syrian government must feel that it is winning. Its strategy, both ruthless and relentless, has paid off. Without Aleppo the Syrian opposition and its foreign backers will have no practical way forward, against a regime that seems more safely embedded in the heartland of the country than at any point in the past five years.

With so much currently up in the air, a new U.S. president on his way into office who has expressed doubts about the Syrian opposition, and the European Union preparing to reorganize its Syria policy, developments in Aleppo could well change the parameters of the Syrian conflict.

The Breakthrough in Aleppo

Starting on November 27, the defenses of Aleppo’s rebel-held area suddenly gave way, allowing the government to try cutting the enclave into two. Fearing encirclement, opposition forces in the northern part of the enclave fled south, while civilians scattered in every direction—some deeper into rebel areas, some toward government-held western Aleppo. The resulting chaos enabled new regime gains. Since then, government forces and their allies have also moved into the southern Sheikh Said district, and as aircraft pummel the city, they are now putting pressure on rebel forces from nearly every direction.

The reasons for this sudden collapse remain obscure. Perhaps there were, as some have speculated, backroom deals and betrayals, or perhaps the rebels were in disarray after infighting earlier in November. In the end the truth may be straightforward: With rebel resources having been depleted by a six-month siege, the insurgents could not hold out against far superior forces.

Still, fighting in a place such as Aleppo is arduous, and it is possible that the government offensive will stall. The Russian government is reportedly still talking to both the United States and to the Syrian rebels about a truce, as opposed to a full army victory, though it seems unlikely that Assad is on board with the idea. The situation could drag on for another round or two—whether counted in days, weeks, or months—with the pro-Assad forces reportedly seeking full control over the city by January. Whatever the timeframe, the final outcome now seems inevitable: Assad will retake eastern Aleppo.

Should this happen it would represent a dramatic defeat, with powerful political repercussions for the Syrian opposition. Though many have sworn to continue fighting, some are likely to conclude that without Aleppo and with Donald Trump in the White House, there is no longer any hope of achieving a victory over Assad.

Erdogan’s Mind is Elsewhere

A defeat in Aleppo will leave the Syrian opposition at a dead end not just because it will have lost its most important piece of real estate, but because the remaining rebel strongholds are of little use as platforms to reverse the tide of war.

The most interesting area is the rebel zone carved out thanks to Turkish military intervention northeast of Aleppo, in battles against the self-proclaimed Islamic State. Here, the prospect of military backing from Turkey’s fiercely anti-Assad president, Recep Tayyip Erdogan, has raised the opposition’s hopes of breaking the siege of Aleppo. But that is unlikely, for three reasons.

First, the purpose of the Turkish intervention was to clear the area from Islamic State jihadis and ensure that the vacuum was not filled by Kurdish forces aligned with the Kurdistan Workers’ Party, or PKK. For all of Erdogan’s loathing of Assad, it doesn’t come close to his hatred of the PKK. Indeed, if Erdogan’s primary concern had been to overthrow the Syrian president, he wouldn’t have diverted thousands of Syrian rebel combatants to help him clean up the border region when they were so desperately needed in Aleppo.

Second, the Turkish intervention was based on an understanding with Russia, which is committed to protecting Assad. How Ankara and Moscow plan to divide the border area is unclear and may be up for renegotiation, and there may well be clashes between Turkish- and Russian-backed forces (perhaps even some friction between Russian and Turkish troops). But we know that neither Russia nor Turkey is interested in a major conflict, having spent so much time improving their relations—and also because Turkey’s NATO membership greatly raises the stakes of any confrontation.

Third, if Erdogan had any intention of breaking the siege of Aleppo, he would have done so long ago. It makes no sense for him to wait until Assad has virtually destroyed the rebel enclave to try saving it now.

After a long and telling silence, the Turkish president recently spoke out on Aleppo, saying his intervention in August had been to “end the rule of the cruel Assad.” Unsurprisingly, this met with immediate Russian pushback, as a Kremlin spokesperson said it would be in touch with Turkey to seek an explanation. The actual explanation? Most likely, Erdogan is simply trying to save face.

If Turkish intentions northeast of Aleppo are not what the opposition had hoped for, Ankara’s involvement in Idlib has so far been more clearly aligned with the rebel cause. The area, which fell completely to Syrian rebels in spring 2015, still receives strong support from across the Turkish border and has served as a staging ground for attacks in Aleppo, Hama, and Latakia.

The Idlib rebellion is strong and well implanted. It is a real threat to Assad. But though it contains many different groups, it is strategically dominated by hardline Islamists such as Ahrar al-Sham and Jabhat Fatah al-Sham, the new incarnation of Jabhat al-Nusra that has links to Al-Qaeda and is riddled with international jihadis. These groups are formidable enemies of the regime, but they are also too toxic to gain Western endorsement. Policymakers in Doha and Ankara have shown a higher threshold of tolerance for jihadism than their colleagues in Washington, but Jabhat Fatah al-Sham is ultimately a step too far for everyone.

In other words, while it will remain a thorn in Assad’s side, the Idlib region is unlikely to serve as the springboard for a foreign-backed strategy to end Assad rule.

All Quiet on the Southern Front

The insurgency in southern Syria relies on groups gathered into a coalition known as the Southern Front, which is more palatable to the United States and its allies. These groups are held on a tight leash by the U.S.-backed, Jordan-based Military Operations Center, and their willingness to play by rules imposed from abroad is what has made them an attractive partner.

But being a proxy force has its disadvantages. The southern rebellion has been virtually frozen for the past year. The battles petered out after Russia negotiated some form of deal with Jordan on Bashar al-Assad’s behalf, which was endorsed by opposition sponsors who worried about chaos spreading to Jordan and Lebanon. Having once hitched their fortunes to foreign funding, the Southern Front rebels do not have many other options.

It is possible, of course, that the Military Operations Center and Jordan will agree to reignite the southern rebellion to compensate for the loss of Aleppo. But even then it beggars belief, given their timid behavior until now and the importance they place on Jordanian and Lebanese stability, that the opposition’s foreign backers would approve of rebel offensives that threaten Bashar al-Assad’s hold on Damascus. And if not that, then what’s the point?

Indeed, around Damascus the regime has made significant advances in 2016 and is now mopping up pockets of rebel territory. The fall of Darayya in August was followed by pressure to surrender on other suburbs and outlying towns. Rebel fighters from the western area of Khan al-Shih have now begun to evacuate towards Idlib, and a similar deal is likely in Al-Tell, north of Damascus.

The main remaining rebel stronghold is east of Damascus in the Ghouta region. However, it is not in good shape. Last spring, the besieged enclave became the scene of severe infighting. Since then, the East Ghouta has been divided. The Syrian regime has so far focused its fire on a Salafi group known as the Islam Army (Jaish al-Islam), seizing large areas in what looks like a deliberate divide-and-conquer strategy. “The Syrian regime is an evil regime,” says a local activist named Alaa, who spoke to me over Skype. “They are constantly trying to create unrest. Sometimes they attack on certain fronts while holding back on others.”

The army is now putting pressure on the Islam Army-held city of Douma to negotiate a ceasefire, as a step towards dismantling rebel control over the East Ghouta enclave. According to a source on the government side in Damascus, truce talks have also started with another rebel group in nearby Harasta. The enclave is larger than eastern Aleppo in terms of territory and population, and it may hold out for some time, but it is difficult to imagine that the rebels will reverse the momentum of the regime.

Poor Prospects for the Opposition

It would be foolish to predict events. The chaos in Syria has a habit of undermining the best-laid plans. Perhaps the always unpredictable Recep Tayyip Erdogan will throw his weight behind a rebel offensive in Aleppo after all.

But going by what we now know, things look bad for the opposition. With eastern Aleppo and the East Ghouta contained and ripe for resolution on the government's terms, Assad seems well on his way to stable control over Syria's core area. If the opposition remains unable to stage a meaningful counter-offensive, he could negotiate or fight his way into new areas, including some of those currently in the hands of the Islamic State.

Of course, much depends on the regime’s own abilities, and it has real weaknesses. It is exhausted economically and short on fighting men. Its failure to engage in constructive compromises or to provide a political opening for opponents ready to shift direction has further cemented its isolation. And yet, at the end of the day, this is a war, and Assad’s military gains on the ground will sooner or later translate into political advantage.