Aleppo siege marks dramatic upheaval on Syrian battlefield

• In the space of a few weeks, the Syrian battlefield has been transformed
• The Assad regime has severed the main road from Aleppo to the Turkish border
• A defining battle for Aleppo, Syria's largest city before the war, seems imminent

(CNN)The images from Aleppo, Idlib and Syria's border with Turkey can be described in one word: despair.

Tens of thousands of people have fled the relentless bombing and shelling that has paved the way for dramatic battlefield gains by the regime of President Bashar al-Assad and its allies. Hundreds of thousands more remain trapped, awaiting their fate with trepidation.

In the space of a few weeks, the Syrian battlefield has been transformed, the balance of forces pulverized and the prospects for peace talks -- already dark -- virtually extinguished. Another tide of displaced civilians converge on the Turkish border, trapped by the advance of regime forces.

Last week, the regime of Bashar al-Assad, supported by Iranian and Lebanese Shia militia, severed the main road from Aleppo to the Turkish border, a narrow corridor through which the rebels and NGOs alike moved supplies. The Syrian Observatory for Human Rights reports that several villages in the area were hit by airstrikes on Sunday.

A defining battle for Aleppo, Syria's largest city before the war, seems imminent. Regime forces and their allies on the ground, supported by Russian bombers in the air, are tightening the noose around the eastern half of the city, still held by a coalition of rebel groups. It's estimated some 320,000 people still live, or subsist, there -- under continual bombardment.

Shortages of diesel and food are reported, but many people simply don't dare or can't afford to leave. One civil defense worker told the Guardian newspaper: "They think, 'We can die in our own homes, we don't need to go to other places to die.' "

Russian revolution

Beyond the humanitarian catastrophe that looms, the plight of Aleppo symbolizes the rapid transformation of the Syrian battlefield since the regime, Iran and Russia came together. For much of 2015, Assad's forces were on the defensive, as rebel groups consolidated and took major towns in Idlib, the Aleppo countryside and began to attack regime strongholds in Latakia.

It was the very real possibility of regime collapse that prompted Russian intervention in September. Russian airstrikes and Iranian militia have since bolstered regime troops and reversed the tide. Aleppo is their most prized target.

"Should the rebel-held parts of the city ultimately fall, it will be a dramatic victory for Assad and the greatest setback to the rebellion since the start of the uprising in 2011," says Emile Hokayem in Foreign Policy.

The Institute for the Study of War says a successful regime offensive around Aleppo would "shatter opposition morale, fundamentally challenge Turkish strategic ambitions and deny the opposition its most valuable bargaining chip before the international community."

Rebel groups have made desperate appeals for help in defending the city.

The notoriously fractious resistance groups are declaring alliances to bolster their collective resistance. One of the most important groups, Ahrar al Sham, announced at the weekend: "We extend our hands to all factions of the Syrian revolution ... and we announce our acceptance for unity with them without any prerequisites."

But even briefly united, they can't shoot down planes, and they don't have T-90 tanks.

Since Russia began its air campaign, most of its strikes have been on cities and towns held by the rebels in western Syria. The aim: to link regime-held territory from the capital to the coast. These are not areas where ISIS has much of a presence; al Nusra, Ahrar al Sham and elements of the Free Syrian Army are the main groups.

Resistance has been fierce, but the sheer scale of the assault has gradually pried one town after another -- or rather their ruins -- from rebel hands.

In the process, senior rebel commanders have been killed in Homs, Idlib and Aleppo provinces.

Some commentators believe that the Assad regime and Russia set out to hoodwink the West by agreeing to the Geneva peace process while stepping up their military campaign, to create "facts on the ground" that would vastly change the balance in the negotiations.

"Their ultimate objective is to force the world to make an unconscionable choice between Assad and ISIS," says Hokayem. For now, ISIS is waiting out the battle for Aleppo and watching its rivals get pummeled. It is crowing that it is the only real defender of Sunni Muslims against the Shia-dominated forces now on the offensive.

The Syrian Kurds, whose attitude toward the Assad regime might be described as ambivalent, also appear to be taking advantage of the situation, chipping away at rebel-held villages north of Aleppo. According to diplomats in the region, they are being encouraged by Russia -- keen to antagonize Turkey at any opportunity.

For Aleppo, read Grozny

Some analysts compare Russian President Vladimir Putin's strategy in Syria with the Russian campaign in Chechnya in 1999, which he directed as Prime Minister. All opposition figures were marked as terrorists, and Russian forces destroyed cities such as Grozny in which insurgents lived, as well as the insurgents themselves. By some estimates, 80% of Grozny was rendered uninhabitable. Human Rights Watch published a report on the Chechen campaign in 2000 entitled "Welcome to Hell" and accusing Russian forces of egregious human rights violations.

Putin pursued an exclusively military solution against the Chechen insurgency, and ultimately it worked. It took six years and an unknown number of Russian military casualties, but today acts of resistance in Chechnya are few and far between, and the republic is run by a Putin loyalist.

The same approach is apparent in Syria. After his meeting with Putin at the United Nations in September, U.S. President Barack Obama said of the Russians' view of the rebels: "From their perspective, they're all terrorists."

But Chechnya is not the only precedent.

Jihadists, some of them from the Caucasus, have threatened to turn Syria into another Afghanistan for the Russians. While they may be driven from territory they hold, they are unlikely to be driven from Syria and could revert to insurgency tactics such as ambushes, assassinations and suicide bombings.

To some analysts, the regime advance will only radicalize what remains of rebel forces in Syria. Hokayem speaks of a "widespread and understandable feeling of betrayal in the rebellion, whose U.S.-friendly elements are increasingly losing face within opposition circles."

Last month, Osama Abu Zeid, a senior adviser to the moderate Free Syrian Army, complained that "the U.S. is gradually moving from a neutral position toward being a partner in crime as it allows Assad and his allies to kill Syrians."

Several rebel groups, as well as Turkish officials, blame Washington for the failure to establish a "safe-haven" inside Syria last year. Some in Washington take the same view.

In an Op-Ed for The Washington Post, two former senior officials, Nicholas Burns and James Jeffries, urge the Obama administration to "dramatically expand funding for the moderate Sunni and Kurdish forces that pose an alternative to Assad's government and the Islamic State" and "reconsider what it has rejected in the past: the creation of a safe zone in northern Syria to protect civilians, along with a no-fly zone to enforce it."

But they acknowledge that "defending the zone, preventing it from being overwhelmed by refugees, grounding it in a convincing legal justification and keeping out jihadist groups would be daunting tasks."

Europe's next nightmare

The United Nations estimated Friday that 40,000 people have already been displaced by the fighting in Aleppo. But the current exodus is by no means the first since the Russian air campaign began. In just three weeks in October, the United Nations reported the displacement of 120,000 people from Aleppo, Hama and Idlib. Nor will it be the last.

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Turkey -- which already has 2.5 million Syrian refugees on its soil -- says it is close to capacity. The European Union is pouring cash ($3.3 billion) into a vastly expanded program to house refugees in Turkey, Jordan and Lebanon, trying to forestall another surge of refugees across the Mediterranean. But it may not be enough.

Some EU officials see Europe's expensive and divisive refugee crisis as an intended consequence of Russian policy.

"Putin likes to cast himself as a man of order, but his policies have brought more chaos, and Europe is set to pay an increasing price," says Guardian columnist Natalie Nougayrède.

A 'painful year'

The main supporters of the rebels in northwest Syria -- Turkey, Saudi Arabia and Qatar -- are now short of options. They could send weapons across the border into Idlib, but the province is largely controlled by al Nusra.

They seem unlikely to walk away from a struggle in which they have invested so heavily and watch their Shia enemies -- Hezbollah, the Alawite-led regime, the Iranian Revolutionary Guard -- claim victory.

Fabrice Balanche at the Washington Institute speculates they may try to "set up a new rebel umbrella group similar to Jaish al-Fatah, and/or send anti-aircraft missiles to certain brigades...(or) open a new front in northern Lebanon."

"The question is, do Riyadh and Ankara have the means and willingness to conduct such a bold, dangerous action?" Balanche asks.

It is hard to find anyone who believes the situation in Syria will get better before it gets much worse.

"The conditions are in place," says Hokayem, "for a disastrous collapse of the Geneva talks -- now delayed until late February -- and a painful, bloody year in Syria."