Damage is seen after what activists said was shelling from forces loyal to Syria's President Bashar Al-Assad, inside Umayyad mosque in Aleppo on March 15, 2014. Reuters

The many and varied groups fighting in Syria’s civil war have long been in a tug-of-war to control the northern city of Aleppo, but the current clashes have effectively lumped the factions in two camps: opposition brigades unofficially aligned with al Qaeda affiliate Jabhat al-Nusra (JAN) or forces aligned with Syrian President Bashar Assad’s regime.

In Aleppo, JAN is part of a joint military operation room with two of the most well-equipped anti-regime rebel brigades in the north: Jabhat Shamiya (the Levant Front) and Jabhat Ansar al-Deen (Supporters of the Religion Front). The two coalitions have pulled resources and manpower from a variety of formerly independent brigades, bringing together hard-line extremist groups like the Islamic Front and the Mujahedeen Army with more secular units of the Free Syrian Army.

On Friday, state-run news agency SANA said Syrian regime bombing had killed JAN’s top military commander, Abu Hommam al-Shami. His replacement has not been announced, but his absence has not slowed JAN’s progress on the ground. JAN led Sunday’s offensive against regime forces in northern Aleppo, where Assad’s fighters have been trying to break the rebel hold since mid-February.

Though JAN is al Qaeda’s only branch in Syria, the group often downplays its role in al Qaeda Central’s long-term plan to establish an Islamic "emirate" in favor of marketing itself as a Syria-centric opposition group focused on the revolution and overthrowing Assad. Their strategy relies on their ability to work alongside opposition groups of varying degrees of extremism when fighting the Islamic State group.

“That dynamic inside of Aleppo city has been well established for quite some time. ... This is how command and control across organizations has been conducted inside of the grinding stalemate of Aleppo city,” Jennifer Cafarella, a Syria analyst at the Institute for the Study of War (ISW), said. “What we are seeing is a decrease in the role that those moderate actors are playing inside those coalitions.”

JAN’s gains in Aleppo were partially due to the group’s ability to neutralize one of its biggest rivals, U.S.-backed moderate rebel group Harakat Hazm. The group unofficially dissolved itself last week and the remaining members joined Jabhat Shamiya, according to ISW.

“There are still groups inside of Aleppo that Nusra would like to target,” Cafarella said. “However, I think Nusra has pushed the envelope as far as it can right now in Aleppo without jeopardizing the defense of Aleppo city, which I don’t think JAN will ever do.”

Rebels in Aleppo also have taken steps toward political unity. In November, 14 rebel brigades formed the Aleppo Revolutionary Council. Earlier this month the group refused to sign a United Nations-brokered ceasefire in Aleppo because the proposal included Assad’s regime.

Lack of funding and infighting within Syria’s myriad rebel groups has turned the trend from small, fragmented brigades to unified coalitions that include a wide spectrum of ideologies — some of which include al Qaeda-backed JAN. In December, around 70 rebel brigades, both secular groups and hard-liners who believe in a fundamentalist reading of Sunni Islam, formed the Revolutionary Command Council to fight the Assad regime and ISIS. JAN, which often acts as a mediator between fighting rebel groups, was among those members, but U.S.-backed Harakat Hazm was not.

In 2013, the Syrian opposition included a large number of Islamist brigades that were neither moderate nor jihadist but were aligned with the Syrian Muslim Brotherhood, under an umbrella organization called the Commission of the Shields of the Revolution. Two years later, the brigades have begun to slowly disperse.

“So far, few battalions have pledged allegiance to the more extremist groups that are currently on the rise in Syria, such as the Nusra Front and the Islamic State,” Raphaël Lefèvre of the Carnegie Institute’s Middle East Center wrote. “But this could be about to change.”

Many of the Shield Brigades defected to groups like Liwa al-Tawhid and Ajnad al-Sham that are members of the Islamic Front coalition fighting alongside JAN in Aleppo.

JAN “prioritizes effective and long-term relationships between JAN and rebels in a way that makes its governance very unique, as opposed to that of ISIS,” said Cafarella. “It’s a core element of their strategy inside of Syria to become a relied upon partner in the fight against Assad. JAN sees itself as the spearhead of the Syrian revolution, but it doesn’t seek to become the Syrian revolution.”