When Jabhat al-Nusra recently expelled several moderate rebel groups from their strongholds in northwest Syria, this triggered rumors that the Al-Qaeda affiliate has concluded a secret alliance or at least a tacit understanding with its main jihadist rival, the Islamic State. James Clapper, the U.S. Director of National Intelligence, correctly dismissed this as unlikely, pointing to the deep divisions between the two organizations. But Jabhat al-Nusra is clearly positioning itself in anticipation of developments on the ground, so the real question is what does it see coming? How does that reflect what it believes—or knows—the Islamic State is preparing to do? And how does that bear on the rest of the armed opposition and on the Assad regime?

Jabhat al-Nusra has built up its military presence and activity in several regions since last summer, when it spearheaded rebel advances towards the central Syrian city of Hama, though they were subsequently pushed back. It has become increasingly active in the Lebanese border region as a result of regime pressure in the Qalamoun region, which has pushed the rebels towards Lebanon. But its gains in Syria’s southern Quneitra province and the western Damascus countryside since September have also enabled it to open new infiltration routes into the Shabaa region and southern Beqaa valley of Lebanon. And in early November it played a central role in wresting the large towns of Nawa and Sheikh Miskin from the regime in northern Houran, due south of Damascus.

These developments do not place the Assad regime or the Syrian capital in imminent danger, but they reveal the rise of Jabhat al-Nusra as the largest and most capable armed group in the south and demonstrate its ability to expand and consolidate. This may also explain Nusra’s pressure on the last border crossing to Jordan held by the regime at Nasib, which Jordanian intelligence had previously kept strictly off-limits to other rebel groups, over which it has very considerable influence. 

In parallel, Jabhat al-Nusra is trying to develop a foothold in Lebanon, where it has roots among some sectors of the population, especially in the north and northeast. This is due to longstanding social and economic interactions with the western Syrian regions that Nusra mainly springs from, and to bonds forged with Lebanese recruits who fought alongside it under the banner of Jund Allah in al-Qusair and other towns of western Homs province. 

However, Jabhat al-Nusra’s behavior in Syria’s Hama and Idlib provinces, where it already has an extensive presence, offers the most significant indication of what it sees ahead. It knew that the moderate opposition had agreed several months ago to fight it in the future, as part of a U.S. effort to eliminate extremists and make a deal with the regime. And so its move against the U.S. and Saudi-backed Syrian Revolutionaries Front and Hazm Movement, in particular, was pre-emptive. But their threat was not imminent, suggesting that Jabhat al-Nusra is preparing to deal with other eventualities. It has become the main rebel force in the northwest, and has the capability to capture the opposition’s last two border crossings to Turkey, vital for rebel training and supply, humanitarian relief flows, and the movement of opposition activists and administrators.

The threat to the moderate wing of the Syrian rebellion is real. But although the Assad regime has taken heart from their discomfit, calculating that the dual rise of Jabhat al-Nusra and the Islamic State will compel the U.S. and its core allies in the Friends of Syria coalition to deal with it, it has little cause for complacency. In fact it has become increasingly vulnerable to the Islamic State, which poses a growing threat at several strategic locations along its eastern flank. 

The Islamic State has not undertaken significant military initiatives elsewhere in Syria since launching its offensive on the Kurdish enclave around Kobane (Ayn Arab) in September, possibly because it is currently stretched. U.S.-led air strikes pose an impediment, but as importantly, any new offensives require advancing across open terrain from the sparsely inhabited and poorly monitored badia (steppe) in the east, into more densely inhabited and heavily guarded areas of central Syria. But the Islamic State has shown an ability to conduct offensive operations under fire, and has been actively recruiting and training in Syria. It is likely to undertake new offensive action sooner or later, whether to expand and consolidate its zone of control, demonstrate its continued vitality, or keep adversaries off balance—or all three. 

The regime’s salient around Aleppo is especially vulnerable: it relies entirely on a narrow land corridor from Salamieh in eastern Hama province to Khanaser in southern Aleppo province, which it does not control fully. The regime has consolidated its defences leading to Khanaser from the strategic Asrieh crossroads, but an advance into northern Homs and Hama provinces could bypass Asrieh and sever the corridor indirectly. The regime is also struggling to regain undisputed control of the gas fields in eastern Homs province, where the Islamic State first seized minor facilities in July. Since then it has taken several productive fields and processing and pumping plants, reducing regime electricity production by 10 percent. 

Potentially as seriously, Islamic State pressure is mounting along the line between Homs, Palmyra (Tadmur), and the regime’s easternmost outpost in the badia at al-Sukhneh. Although regime defences around these main points are dense, the Islamic State could still inflict major psychological damage by skirting around them towards Qalamoun, threatening to cut off regime garrisons there and in far to the east in Deir az-Zor. Even if the Islamic State does not make lasting territorial gains, going against high-value regime targets offers disproportionate rewards and an opportunity to acquire strategic leverage. 

Conversely, the Islamic State could prioritize retaking the foothold it had in opposition-held territory in Idlib and Aleppo provinces until January 2014. This would pose a direct challenge to Jabhat al-Nusra’s military position, and to its control of an autonomous population and economic base. Whether Jabhat al-Nusra estimates that the Islamic State can and will pursue this objective or is too stretched to make the attempt, it is strengthening its own position while it can. This means establishing territorial contiguity between its zones of control, eliminating or neutralizing potential challengers from within, and projecting an image as a powerful and capable force to be reckoned with. 

So far, Jabhat al-Nusra has built on the surge of sympathy among the local population in response to the U.S. strikes against it. It remains a notably decentralized organization, however, and so how its local commanders will respond to other rebel groups on the one hand or the Islamic State on the other will vary from one region to another. Jabhat al-Nusra may not intend to declare an emirate anytime soon, but as it creates new facts on the ground and consolidates territorially and administratively, it will increasingly look like one. A major new offensive by the Islamic State could force its hand, compelling it to choose between accepting junior status in a partnership or confronting its powerful rival, each of which carries the risk of its own breakup. 

This article was originally published in Arabic in Al-Hayat.