The fall of Aleppo would solidify Assad militarily and confirm that Moscow was now the go-to actor for much of the region. Political rehabilitation for Assad is more difficult because of the scale of his crimes.
The pro-Assad coalition in Syria has conquered more than a third of the rebel-held enclave in eastern Aleppo City, the last urban stronghold of the mainstream armed opposition. Without significant external assistance, it is difficult to imagine the rebels can hold off, and in the coming days or weeks will likely be forced out entirely. This will not end the war, nor will it suppress the opposition, but it will end the rebellion as a strategic threat to the regime of Bashar al-Assad and push the insurgency into a greater reliance on extremists, creating more space for international terrorists and protracting the war.
The pro-Assad coalition in Aleppo consists of Russian and Syrian regime air power, with ground forces led by Iran, patched together out of the battered remnants of Assad's security forces and an international brigade of rabidly sectarian Shia jihadists.
In February, under the cover of negotiating a ceasefire, the pro-Assad forces cut off Aleppo City's last supply line into Turkey and in July they besieged the rebel-held areas in east Aleppo City. The insurgency briefly broke the siege, but it was re-imposed; a second insurgent offensive had some initial successes before being defeated earlier this month.
The regime's siege-and-starve tactics, which have defeated Homs City and rebel-held suburbs around Damascus, then began. Civilian infrastructure was devastated. No food deliveries have been allowed for four months. All of this was justified by a claim that terrorists held the city, when in reality al-Qaeda's rebranded Syrian branch made up only 2.5 per cent of the insurgents in Aleppo City.
Having exhausted the rebels and civilian population, the pro-Assad forces prepared a final assault, which began Sunday. By Monday, with a little help from the Syrian PKK—not unlike the sequence of events in February—the pro-Assad coalition made rapid gains in Aleppo City, capturing the northern third of the rebel-held pocket.
Absent rapid, extensive external help, the rebellion almost certainly cannot avoid the loss of the rest of its territory in Aleppo City, and since the only forces who could thwart the pro-Assad coalition, namely the United States and Turkey, have been neutralized by Russian diplomacy, this seems unlikely to occur.
Russia's objectives when it intervened in September 2015 were to secure Assad militarily in power, rehabilitate Assad politically by eliminating all workable opposition elements, and to recast the regional balance of power away from American hegemony.
The first and third objectives were more or less secured after the first three months of the intervention, and Moscow's conduct during that time—using rhetoric about fighting the Islamic State to systematically attack the U.S.-supported moderate rebels—put it well on the way to accomplishing the second objective.
What the fall of Aleppo means for the Syrian opposition
The fall of Aleppo would solidify Assad militarily and confirm that Moscow was now the go-to actor for much of the region. Political rehabilitation for Assad is more difficult because of the scale of his crimes and because mainstream sections of the rebellion will outlast the fall of Aleppo.
One of the immediate ways that the regime is trying to manoeuvre its way back into the family of nations is by having funds for reconstruction from international institutions released into its hands. This was part of the purpose of the recent propaganda conference in Damascus. Politically, this would be a recognition that Assad was staying, and more practically it would ease Assad's re-imposition of his rule after his genocidal war against the population. Somewhat beyond obscene as this is, states are cold beasts and Aleppo's fall would bring some governments around to finding a modus vivendi with the dictator.
For the revolution, this realpolitik calculation that Assad is irremovable short of external invasion will mean the end of some foreign support as states cut their losses. The foreign backers of the rebellion who continue after Aleppo—and especially if the new U.S. President, Donald Trump, formalizes the U.S.'s de facto pro-Assad policy and repudiates the rebellion entirely—will find their options further constrained to ever-more-extreme forces.
The jihadi-salafists who maintained from the start that the U.S. was conspiring with Assad against the largely-Sunni rebellion would appear politically vindicated by Aleppo's fall, and in sheer military terms al-Qaeda could co-opt large numbers of those who want to continue the resistance to Assad.
Turkey's intervention, which mobilized rebels to inflict considerable damage on the Islamic State, is an opportunity to bolster a mainstream rebel force and therefore to also degrade al-Qaeda by offering the insurgency a real, on-the-ground alternative. It has already borne fruit. But if Aleppo falls, the Turkish operation will be discredited for standing on the side-lines as the revolution's hopes of removing Assad were defeated. Al-Qaeda did at least try to break the siege.
Though the population in east Aleppo risked bombardment rather than flee because of the fear of Assad's prisons, where death would be the least of their problems, once the city is reconquered it is likely that many people will leave rather than face retribution for "collaborating with terrorists". Further refugee flows, from the fall of Aleppo itself and from the certainty that will bring that the five million people already driven from Syria will never return, will exacerbate tensions in neighbouring states and reinforce the dynamics in Europe that have led to the rise of populist, far-Right forces friendly to the Kremlin.
Inside Syria, the sense of betrayal will make it very difficult to restore the mainstream revolutionary forces whose cause is seen as attached to Western power to primacy in the insurgency; the West will be seen as complicit, if only by omission, in the horrors that are surely to come in Aleppo. This will strengthen al-Qaeda and other groups who cannot be negotiated with. On the other side, the regime's battlefield successes will—despite is inability to in fact restore total control—give it even less reason than it has now to negotiate.
Put simply, Aleppo's fall will not pacify Syria; it will see the spread of radicalism and chaos inside the country and well beyond for a long time to come.