The Islamic State of Iraq and al Sham has even directly clashed with another al Qaeda-linked jihadist group, Jabhat al-Nusra. In one of the most prominent clashes between the groups, fighters from the Islamic State of Iraq and al Sham attacked the Jabhat al-Nusra regional headquarters in Shadadi, killing members of the other jihadist group and seizing weapons and oil production equipment. Jabhat al-Nusra was not in a position to defend itself, as most of its fighters in the region reportedly were on the front line, fighting Kurdish YPG militants.
The Islamic State of Iraq and al Sham's attacks on Free Syrian Army units largely are related to the jihadist group's fears that more moderate rebel factions and the West will join forces against it. Its attacks on Jabhat al-Nusra are not as clear cut, but could be linked to local power dynamics and broader differences in outlooks between the two jihadist groups. The leadership of the Islamic State of Iraq and al Sham and a substantial number of members are foreign-born, and this — along with the leadership's extremism — has driven a wedge between the group and the Syrian locals.
Overall, the Islamic State of Iraq and al Sham's actions in recent months have created a backlash against it from other rebel groups and fueled a resurgence by Jabhat al-Nusra. Hundreds of fighters from the Raqqah-based 11th division, previously affiliated with the Free Syrian Army, joined Jabhat al-Nusra on Sept. 19.
The Free Syrian Army's position in the jihadist-filled governorate of Raqqah was already tenuous at best. The switch very likely was motivated at least in part by the fighters' desire to enhance their survivability by coming under the protection of Jabhat al-Nusra. Indeed, a new Jabhat al-Nusra recruit reportedly said in an interview with AFP that, "Al-Nusra is fighting to bring down the regime, while ISIS [the Islamic State of Iraq and al Sham] fights to bring down the FSA [Free Syrian Army]."
Besides clashes among different rebel groups in Syria, there have even been splits among groups allied with the Islamic State of Iraq and al Sham. A splinter group of Chechen fighters that had been part of Jaish al-Muhajireen wal Ansar, a group affiliated with the Islamic State of Iraq and al Sham, claimed in a Sept. 4 video to have formed a new unit called the Mujahideen of the Caucasus in the Sham and left the Islamic State of Iraq and al Sham-affiliated group due to its extremism. Jaish al-Muhajireen wal Ansar, on the other hand, claims that the splinter group was banished due to corruption. Regardless of the real reasons behind the split, it highlights the tensions that exist even within groups affiliated with the Islamic State of Iraq and al Sham.
Rebel infighting in Syria is not new. Indeed, the disparate natures of the rebels have all but ensured considerable friction between the groups related to conflict over power, territory, resources and ideology. With the rise of the Islamic State of Iraq and al Sham, however, rebel infighting has gradually intensified and has measurably affected the broader rebel fight against the Syrian regime. On occasion over the past few months, rebel units from various factions have elected to leave the front line fighting against government forces to protect their turf in rebel-controlled territory against other encroaching rebel groups. The rebel infighting has led to a diversion of resources almost equal to that caused by the intensified Syrian rebel showdown with the Kurdish YPG.
As the Islamic State of Iraq and al Sham's actions continue hampering the wider rebel fight against the Syrian regime, rebel groups — even those who have fought alongside the Islamic State of Iraq and al Sham in the past — are increasingly denouncing the group. Because of the nature of the Islamic State of Iraq and al Sham and its leadership, the group will very likely continue lashing out at all of its perceived enemies, thus weakening the rebellion further and contributing to the growing strength of other groups such as Jabhat al-Nusra.