IRBIL, Iraq — When the fighters of the Islamic State of Iraq and Syria swept aside Iraqi security forces in just two days of fighting to seize control of much of northern and central Iraq, it appears they also took control of the initiative in their fight in neighboring Syria, where they’ve seen recent successes against rivals who once considered them allies.
The gains in Iraq, analysts and experts say, not only included huge amounts of weaponry and ammunition that also could be used in Syria but also provided a powerful message to members of other Syrian militant groups that ISIS was a group on the ascent. That, experts say, is likely to bring it new recruits from Syrian rebel groups whose ideology is really not much different from ISIS’s.
Aaron Zelin, who edits the Jihadology blog and studies Syrian rebel groups, said that was particularly true of the Nusra Front, an al Qaida affiliate that’s been at the forefront of rebel successes against forces loyal to Syrian President Bashar Assad, and Ahrar al Sham, one of the primary groups that form the Islamic Front rebel coalition.
“There’s not a lot, if any, ideological difference between ISIS and the Nusra Front or Ahrar al Sham,” he said. “So defections are occurring.”
How that will affect the war to topple Assad is still to be seen. ISIS’s goal of establishing an Islamic state takes precedence over toppling Assad, though the Syrian leader, in ISIS’s view, must go, too. But defections to ISIS’s side will make the dividing line starker between rebel groups that are acceptable to the United States and those that are not. In the end, the least militarily capable rebels may be the ones who aren’t affiliated with ISIS.
“The Islamic Front in general is under considerable pressure right now from a number of directions inside and outside of Syria,” said Charles Lister, who studies Syrian rebel groups as a researcher at the Brooking Institute in Doha, Qatar. One of its key components is Ahrar al Sham, whose ideology makes its members susceptible to joining ISIS.
ISIS, which began its existence as an al Qaida affiliate battling the American occupation of Iraq, has transformed into a self-sustaining proto-caliphate intent on destroying not only its state enemies in the region _ Iraq and Syria _ but also any groups that don’t precisely adopt its ideology and tactics. Since January, it’s been locked in combat not just with the U.S.-backed moderate Free Syrian Army but also with Nusra and Ahrar al Sham.
While ISIS initially lost some territory in central Syria, it also received an influx of recruits, including almost all the experienced foreign jihadis who were fighting alongside Nusra, including primarily Chechen units and a Saudi group.
“Some of it is that they’ve done a better job in terms of fighting and supporting their fighters with equipment, money and ammunition,” said Zelin. “And because of their more excessive aspects, they’ve been in the media all the time, which motivated many of the foreigners to join. Now we’ve seen almost all of the foreigners once fighting alongside Nusra (and Ahrar al Sham) having defected to ISIS.”
Zelin said Nusra and Ahrar al Sham had been quiet recently on social media compared with ISIS, leading to suspicions that they were suffering from internal problems, including a lack of fighters and diminished resources as ISIS appeared to grow.
Lister said ISIS was well positioned to capitalize on the notoriety and publicity surrounding its success in Iraq and that might lead to more power in Syria.
“The spectacular nature of ISIS’s offensive and successes in Iraq has caught the attention of huge numbers of potential recruits around the world,” he said. “But after all, there are thousands in Syria for whom joining ISIS represents only a small task.”
“The cycle of success is amplifying for ISIS: They gain more ground, get more publicity and more recruits,” according to Zelin.
In a crucial three-way fight among Nusra, ISIS and the Syrian government for control of the eastern Syrian city of Deir el Zour, ISIS seems to have the upper hand. While Nusra still controls the city, four of its top commanders defected to ISIS as it was able to bring to bear heavy weapons and armored vehicles captured in Mosul, according to Osama Abu Zeid, a rebel commander who spoke with the activist website Syria Direct.
“ISIS took control over rebel-held areas in the rural areas some days ago,” he was quoted as saying. “All the neighborhoods in the city are under blockade except the al Qusour and al Joura neighborhoods, which are under regime control. Airplanes and artillery continually bombard the blockaded neighborhoods.”
In the northern province of Aleppo, where rebel forces largely had expelled ISIS, the group used its newly captured American equipment to retake the towns of Abla, Tel Gaghan, Cassar, Thelthana, Thelathina and al Barroza from the Free Syrian Army over the weekend, according to local activists McClatchy contacted.
On Sunday, ISIS used American-made Humvees to push Nusra and Ahrar al Sham fighters from the villages of Eksar and Maalal, which strategically sit next to the border with Turkey, according to the Syrian Observatory for Human Rights, a Britain-based group that monitors violence in Syria.
Lister thinks that despite ISIS’s resurgence, the Syrian opposition will continue to press its efforts to topple Assad. He notes that Iraqi militias that had been supporting Assad are returning to their own country to battle ISIS there and that Hezbollah, the Lebanese Shiite Muslim militant group that’s backed Assad, shows no interest in replacing them in Syria.
“A substantial ISIS presence in eastern Syria and western Iraq looks to be a long-term reality, but this doesn’t existentially threaten the capacity of Syrian opposition forces from continuing their fight against the government,” he said.
Prothero is a McClatchy special correspondent. Email: email@example.com; Twitter: @mitchprothero