Why a Turn in the Battle for Aleppo Could Change Syria's Future

— -- The years-long standoff between government forces and rebel fighters in the northern Syrian city of Aleppo appears to be breaking in favor of the Syrian army.

For much of Syria’s five-year civil war, forces loyal to President Bashar al-Assad have carried out relentless attacks and aerial bombardment of the eastern part of the city, long controlled by rebels.

But a recent Syrian army offensive, with Russian military support, appears to have ended the stalemate for control of the city, Syria’s largest before the war.

The defeat of rebel forces in Aleppo could be a turning point in the Syrian civil war, both on the battlefield and for potential talks to end the fighting.

ABC News looks at the recent developments in the long-embattled city.

Who Is Fighting in Aleppo?

Before the war, Aleppo was home to an estimated 2 million civilians, about 250,000 to 275,000 of whom live in areas held by anti-government forces who have been the focus of intense airstrikes and artillery bombardment.

The battle for Aleppo began in 2012 when rebels attempted to seize the city from government forces. The rebel force includes a mix of moderate groups like the Free Syrian Army and Islamic extremist groups like the Nusrah Front, but it does not include ISIS. What resulted was a divided city with government forces in the west and rebels in the east.

Since early this year, regaining full control of the eastern half of the city has been a priority for the Assad regime. With the help of Russian military airstrikes and Iranian and Hezbollah ground forces, Syrian army offensives have steadily made progress in surrounding rebel forces.

Two weeks ago, Syrian forces pushed into rebel-held areas and resumed an air campaign that included civilian targets and health care facilities.

Why Is There a Turnaround in Aleppo?

The renewed fighting around Aleppo began this summer with the Syrian army encircling rebel fighters in the eastern half of the city.

The Syrian army began an offensive in September supported by a relentless aerial bombardment of eastern Aleppo. A cease-fire in October was never fully implemented, and it is believed that the Syrian army took advantage of the cease-fire to continue to build up its forces around rebel groups in the area.

The fighting resumed in mid-November as Syrian army forces pushed into rebel-held areas.

A statement from the Russian Defense Ministry released on Monday said Syrian government troops have recaptured roughly 40 percent of eastern Aleppo.

What Could an Assad Victory in Aleppo Mean?

Defeating the rebel groups in Aleppo would be a major turning point in the Syrian civil war, delivering a major blow to rebel groups in northwestern Syria — a key goal of the Assad regime.

The holdout by the rebels in eastern Aleppo has served as a rallying cry for other anti-Assad groups that have looked at their resistance as a sign that the Syrian military was vulnerable on the battlefield.

On-and-off peace talk efforts ended in November after Russia declared that rebel fighters were violating the cease-fire. Regaining full control of the city would favor the Assad regime at any future peace talks.

The United States and other Western countries prefer a negotiated end to the civil war that would include Assad's stepping down. That position seemed more tenable a few years ago, when Assad's forces seemed unable to overcome rebel groups in central and northern Syria.

But since the Russian air task force and advisers arrived in Syria last fall, the situation has changed. The U.S. sees Russia's involvement as a critical development in the conflict; with his now strengthened hand, Assad will likely press for a negotiated settlement that would leave him in power.