In the past week, the Nusra Front—a Syrian affiliate of al-Qaeda—has attacked rival factions in northwestern Syria, capturing headquarters, bases, and arms stockpiles belonging to both the Syria Revolutionaries’ Front (SRF) and the Hazm Movement. Both groups are considered mainstays of the Free Syrian Army (FSA), a nebulous network of Western-, Turkish-, and Gulf-funded factions. And they are among the best-known examples of the moderate rebels that the United States seeks to vet, train, and equip to take on Syrian President Bashar al-Assad and anti-Western jihadi factions in the opposition.

Responding to the Islamic State Challenge

The Nusra Front has had a rough year, suffering military setbacks, defections, and an ideological crisis. The main cause is the rise of the extremist jihadi faction known as the Islamic State, also known as ISIS or ISIL. Early this year, the Islamic State ended its previously ambiguous relationship with al-Qaeda and entered into open conflict with the Nusra Front and other Syrian factions.

While it was quickly expelled from the Syrian-Turkish border regions of Latakia, Idlib, and Aleppo, the Islamic State compensated by capturing new territory in both Syria and Iraq. These gains included the city of Mosul—which was taken in June, right before the Islamic State declared itself a caliphate—and since then the power of the Islamic State has grown in Syria and Iraq. During spring and summer 2014, Nusra Front forces were expelled by the Islamic State from their strongholds along the Euphrates River, losing access to oil fields that had been important for funding battles and paying fighters.

This has led to internal problems, with leading members reassigned to new positions and increasing defections to the Islamic State. The Nusra Front still seems uncertain about how to respond to the challenge. But in some areas, notably Idlib, the group has begun asserting itself and seizing territory from rival rebel forces, not unlike the way the Islamic State acted in 2013.

Capturing the Borderlands

Since the summer, the Idlib wing of the Nusra Front has embarked on a campaign to implement sharia law along the Turkish border, targeting criminal gangs and small rebel factions alleged to be involved in robberies and extortion rackets. Many of these groups belonged to the FSA-linked SRF, which receives most of its support from Saudi Arabia. Picking off the smaller factions one by one and responding to a genuine popular desire to get rid of rebel criminality, the Nusra Front was able to seize towns like Harem and Darkush and extend its influence along the border.

Major clashes between the Nusra Front and the SRF began in September, but other groups intervened, and the conflict ended in a ceasefire agreement. Immediately after that, the U.S. Air Force attacked the Nusra Front and associated al-Qaeda targets in northwestern Syria. This added to the tension, since the Nusra Front is of course well aware of the U.S. relationship with the SRF and the Hazm Movement and knows that these groups are being groomed to destroy it.

Capturing Maarouf’s Home Town

Now, the violence has resumed with a vengeance. What sparked the fighting remains murky, but the outcome is clear: the Nusra Front has struck a powerful blow at its rivals. In the Aleppo region, skirmishes between the jihadis and the Hazm Movement in late October ended in a deal agreed to by several local factions, whereby the Hazm Movement surrendered its bases and checkpoints west of Aleppo to the Mujahideen Army, another non-jihadi group that receives support from abroad. In Idlib, mediation efforts failed and the Nusra Front overran the SRF’s bases in the Jabal al-Zawiya region—including the village of Deir Sinbel, which is the home village of SRF leader Jamal Maarouf.

The SRF has fought back as best it can, with one of its commanders recently announcing that he had captured more than a dozen Nusra Front sympathizers in northern Hama. Maarouf has appeared in a video statement where he slams the Nusra Front as being made up of traitors and murderers, portraying the group as a tool of the regime and as being as extreme as the Islamic State. Maarouf claims that “we withdrew from Deir Sinbel to save the blood of civilians” and he insists that the war is not over: “God willing, we will liberate Jabal al-Zawiya village by village.”

In fact, the capture of the SRF strongholds in Jabal al-Zawiya must be a devastating blow to Maarouf and his local allies. It also means that, given the scale of the SRF’s losses, reconciliation would seem significantly more difficult than in September.

The end result of the recent violence is that the Nusra Front now appears to be the single strongest faction in northwestern Syria. Of course, one must not forget that there are plenty of other FSA-aligned or independent Islamist factions left to challenge it—but this certainly shifts the power on the ground in Syria.

With the Nusra Front now consolidating its control over key regions in Idlib and proving that it can and will crack down on those who oppose it, the insurgency’s funding sources hang in the balance. The Nusra Front may at some point decide to muscle in on the lucrative operations of the Bab al-Hawa border crossing located further north in the province or seek to control the roads leading there. If Syria’s al-Qaeda franchise manages to dominate this crucial logistics hub, it would make the provision of military, economic, and other aid for non-jihadi rebels significantly more difficult, and it could fatally undermine the current U.S. strategy in Syria.