With ISIS essentially forced from its major strongholds in Iraq and losing its primary stronghold of Raqqa in Syria, the remnants of the group may well make its last stand in eastern Syria's Deir ez-Zor region.

“I don't believe ISIS will be able to hold out for another year,” Professor Joshua Landis, a frequently cited expert on Syria and the head of Middle East Studies at Oklahoma University, told Rudaw English. “However it is possible that ISIS leaders may be eyeing Deir ez-Zor as their last major redoubt.”

Unlike the city of Raqqa, ISIS never managed to seize the entirety of Deir ez-Zor's provincial capital. Soldiers of the Syrian Arab Army (SAA) have held and the airport and surrounding areas for nearly three years now, preventing the group from overrunning the entire city. The US-led coalition is also targeting the militants there, vowing to “give no sanctuary” to them. 

The US-backed Kurdish-led Syrian Democratic Forces (SDF) have also voiced their intent to rout ISIS from that eastern province and have already set up the Deir ez-Zor Military Council to take control of that region if they are the ones who manage to force ISIS out. Late last month the SDF told Reuters that this operation could begin “within several weeks,” possibly even before the current Raqqa operation concludes. An SDF commander also estimated that it will take them another two months to capture all of Raqqa. At present they hold over half of the city. 

Deir ez-Zor is much further south from SDF positions than Raqqa, meaning they will have to extend their supply lines about 150 kilometers from Raqqa itself to fight the militants there. 

The SAA, meanwhile, has begun an offensive against ISIS there. Given its lack of manpower, which it has been supplementing with militias in recent years, and the fact its enclave in the city remains under siege, this could also take time. 

This state-of-affairs consequently leaves ISIS with swaths of territory it can retain hold over, even after losing all of Raqqa, for the foreseeable future since no sizable ground force are yet challenging them there. 

In Landis' reading, “It makes sense for ISIS to choose Deir as its fall back position. Clearly US power is most active and capable in Iraq. The bruising campaign for Mosul proved that the US and its capable Iraqi allies would go to any lengths to destroy it.”

“Syria is a different question,” he added. “The battle for Raqqa is fierce and the US has broken many eggs in order to arm up the Kurds and the SDF. All the same, Deir ez-Zor offers ISIS several advantages over alternative places for a last stand.”

The SDF, in Landis’ estimates, are not yet “prepared for an immediate campaign down the Euphrates” towards Deir ez-Zor. 

“Coalition leaders have declared that they are content for the SAA to retake Deir and Al Bukamal,” he explained, referring to the Syrian border town. “The SAA has been moving slowly to retake central Syria from ISIS, but has not engaged in serious urban warfare against it yet. ISIS may calculate that the SAA will be much more vulnerable to their tactics than the US, which has superior technology, artillery, intelligence, and airpower.”

Given this lack of a formidable ally on the ground, what ISIS will have to contend with in Deir ez-Zor is keeping the SAA enclave there under siege, or make more attempts to destroy it, and enduring ongoing airstrikes, and perhaps some special forces raids targeting their leaders. Until a formidable adversary on the ground mobilizes in their vicinity and moves in to completely uproot them, as the SDF are doing in Raqqa, ISIS will likely remain in some capacity in the Deir ez-Zor region. 

“The battle for Tel Afar suggests that ISIS is losing its command and control and may no longer be capable of the sort of sustained urban warfare that it engaged in in Mosul,” Landis concluded. “But we cannot be sure that the leadership isn't trying to conserve and husband its resources for the battle of Deir ez-Zor.”