Over the past few weeks, the news has been rife with reports of infighting between the Islamic State of Iraq and the Sham, an al Qaeda affiliate, and other Islamist groups in Syria, including al Qaeda’s other Syrian affiliate, the Al Nusrah Front. The Syrian Observatory for Human Rights, an opposition activist observer group, claimed yesterday that 1,069 people have been killed in clashes between rival Islamist groups from Jan. 3 to Jan. 15 in northern and eastern Syria. That figure includes some 130 civilians, as well as 312 ISIS fighters and 608 combatants from what the SOHR calls “the Islamist and non-Islamist rebel battalions.”

During this same time period, the forces of President Bashar al Assad have been able to capitalize on the disarray and make gains, particularly around Aleppo, after the ISIS withdrew from certain areas. The rebel infighting is a boon to regime forces and clearly detrimental to the overall strength of the Syrian opposition.

The dynamism of this conflict within a conflict has made it difficult to follow, as reports of shifting allegiances among the ranks of rebel fighters complicate the picture. In its broad outlines, the fighting among the Islamist groups in Syria appears to constitute a general reaction against the brutal excesses of the ISIS. The apparent triggering event for the clashes was ISIS’ alleged torture and murder of a Syrian doctor affiliated with the Islamist group Ahrar al Sham, which is part of the largest coalition of Islamist fighters in Syria, the Islamic Front, formed in November. Since that incident, ISIS has battled intermittently with various Islamist groups, including the Islamic Front, the Al Nusrah Front, the Ahrar al Sham, and others, such as the newly-formed Muhajideen Army.

The Al Nusrah Front’s dispute with the ISIS epitomizes the complexity of the disagreements within the jihadist factions. While the emirs of the Al Nusrah Front and the ISIS have been at odds since last year when the ISIS attempted to put Nusrah under its banner, their rivalry has not led to open warfare. But the ISIS’ heavy-handed tactics and refusal to submit to combined sharia, or Islamic law, councils, have brought the two groups to blows in some areas. Most recently, Al Nusrah lambasted the ISIS for executing Nusrah’s emir for Raqqah. But even while berating the ISIS, Al Nusrah has offered an olive branch, calling for the group to submit to sharia councils with other Islamist units.

Yet at the same time, ISIS seems to be cooperating and even collaborating with the Islamist groups in various theaters across the country. As Islamist fighters, they share the same goals and a common enemy in the Assad regime.

Given the mix of infighting and cooperation between the Islamists, as well as attempts by the Al Nusrah Front to mediate the conflict and a hesitancy by the Islamic Front to openly declare war on the ISIS, at the moment the current internecine warfare is a complicated affair.

The following is a chronology of the recent internecine battle, including [in italics] instances of cooperation or at least toleration between the ISIS and some of the Islamist groups against which it has also fought:

Jan. 1: The SOHR reported that its network of sources is increasingly being threatened by Islamist extremists, but declined to identify them. They were later identified as the ISIS.

Jan. 2: The Syrian National Coalition charged that the ISIS is linked to the Assad regime and serves its interests. An opposition activist group said the body of a British doctor who had been allied with the Islamic Front’s Ahrar al Sham but executed by ISIS was recently handed over in a prisoner exchange. The Islamic Front demanded that the ISIS perpetrators be brought to justice by a sharia court for the doctor’s death. ISIS released a video clip on the creation of an Islamic state and Osama bin Laden blessing its predecessor group ISI, and the Al Nusrah Front released a lengthy video on its joint operation with the Islamic Front and the Fajr al-Sham Islamic Movement in the capture of an Aleppo hospital.

News emerged that ISIS had taken over Fallujah and Ramadi in Iraq over the past few days.

Jan. 3: A mass demonstration against both the ISIS and the Assad regime took place in Aleppo city. ISIS clashed with rebel groups in various locations in Aleppo province. The Islamic Front and the Syrian Revolutionaries Front called on ISIS to leave the town of Atareb in Aleppo. The Islamic Front denounced ISIS crimes, and the Mujahedeen Army declared ISIS an enemy. Islamist brigades sent reinforcements to the ISIS-controlled Bab al-Salama border crossing by Azaz city. In Idlib, ISIS forces fired on a demonstration and sieged several field clinics.

Jan. 4: The Al Nusrah Front released video of leader Abu Muhammad al-Julani’ conducting a battlefield tour in Aleppo. The ISIS clashed with various rebel groups in Aleppo, and an ISIS commander is said to have been killed in Azaz. ISIS warned rebels that unless they stop attacking ISIS, release ISIS captives, and remove checkpoints, ISIS will withdraw from the liberated areas of Aleppo, leaving them to regime forces. ISIS executed a rebel captive in Idlib and reportedly killed other captives when its fighters were besieged by rebels. The Syrian National Coalition said it “fully supports” Free Syrian Army efforts to combat ISIS in Syria. A newly formed Islamist alliance of eight groups that calls itself the Army of the Mujahideen announced its opposition to ISIS. The Secretary General of the Free Syrian Army claimed that ISIS is “trying to hijack the Syrian revolution.”

Jan. 5: The ISIS clashed with rebels and Islamist battalions in Raqqah. Kurdish YPG forces battled ISIS, Al Nusrah Front, and Islamist battalions in Hasakah. Regime forces clashed with Al Nusrah and Islamist battalions in Deir Izzour. Al Nusrah is reportedly mediating between ISIS and several rebel battalions in Aleppo: several ISIS bases were surrendered to Al Nusrah. Yesterday 10 captive regime soldiers were executed by Al Nusrah and an armed Islamist movement in Aleppo. Some 60 fighters were killed in clashes between Islamist and non-Islamist rebel groups in Aleppo, Idlib, Raqqah, and Hama. Syrian opposition sources say that despite clashes between ISIS and other groups, there does not appear to be all-out confrontation.

Jan. 6: The ISIS clashed with the Syrian Revolutionaries Front and the newly formed Jaish al Mujahideen in al Tabqa in Raqqah. Islamist and non-Islamist rebels also fought against ISIS in other Raqqah cities, and released 50 captives from an ISIS prison in Raqqah city. ISIS clashed with rebels in Aleppo, and an ISIS suicide car bomber detonated near Sha’ar. Islamist and rebel battalions took over ISIS’ main base in Jarabalus in Aleppo. Al Nusrah battled Kurdish YPG forces in Hasakah. ISIS fighters withdrew from Kafarzeita in Hama after mediation by Al Nusrah. Al Nusrah claimed it liberated a Deraa hospital on Jan. 1 with help from a number of Islamic brigades. A top-tier jihadist forum called for support for ISIS and warned that enemy elements on Twitter are trying to sabotage ISIS.

Jan. 7: The head of the Al Nusrah Front called for a ceasefire between the ISIS and clashing rebel groups in Syria, the creation of an independent Islamic council to mediate disputes, and the exchange of prisoners. An opposition activist group said that 274 people have been killed in four days’ fighting between ISIS and rebel groups, including at least 99 ISIS fighters, of whom 34 were executed by rebels. Over 100 ISIS fighters are said to be besieged by rebels in Aleppo and to have asked Al Nusrah to mediate. In Deir Izzour, ISIS fighters withdrew from their base in al-Mayadeen and headed toward Raqqah city. ISIS clashed with Al Nusrah and rebels, including the Kurdish Front Battalion, in Raqqah province. ISIS fighters, backed by Al Nusrah and rebels, captured two towns and several villages in Hasakah from Kurdish YPG fighters, who retreated. At least 34 non-Syrian fighters from ISIS and Jund al-Aqsa were executed by rebels in Idlib; ISIS killed tens of rebels in a suicide bombing near Derkosh yesterday.

Jan. 8: After the Al Nusrah Front called for a truce between clashing rebel and Islamist groups, Abu Muhammad al-‘Adnani, the spokesman for the ISIS, issued a statement denouncing the Syrian National Coalition and the Supreme Military Council as apostates and enemies unless they stop fighting the mujahideen. Al-‘Adnani also warned that ISIS would defend itself from attack, especially from the “Army of the Mujahideen,” a coalition of eight rebel groups, saying ISIS would “crush the conspiracy in its cradle.” An opposition activist group reported that Islamist rebels have taken over ISIS headquarters in Aleppo city, finding prisoners and the bodies of nine executed men, but the fate of the “hundreds” of ISIS fighters there is unknown. The activist group also said ISIS set off car bombs against rebels in Aleppo, Idlib, Hama, and Raqqah.

Jan. 9: The ISIS clashed with Islamist and non-Islamist rebels in Raqqah, Idlib, and Aleppo, and is said to be preparing numerous suicide attacks in Deir Izzour. In Hasakah, ISIS and rebel groups, including the Islamic Front, issued a joint declaration creating a unified sharia council and a joint operations room. In Hama, a truck bomb detonated near a school in the mainly Shiite town of Kalat, killing at least 18 people, and an Egyptian ISIS commander defected to Al Nusrah. Former ISIS prisoners alleged horrific crimes on the part of their captors, including summary executions and torture. Delegates from Syrian opposition groups, including the Islamic Front, met in Cordoba, Spain, in advance of the Geneva II talks. An Arab news outlet said on Jan. 7 that “highly delicate” negotiations were underway between rebels and ISIS in Raqqah for control of the Sed Tishreen prison, where French journalists and an Italian priest were reportedly being held.

Jan. 10: Islamist battalions and the Al Nusrah Front clashed with the ISIS in Raqqah city; ISIS made gains in the city. An opposition activist group claimed that some 500 people, including 85 civilians, have died in clashes between ISIS and Islamist and non-Islamist groups over the past week. A senior Al Nusrah commander said the group has been providing weapons and cars to the ISIS to assist in its battle against the Iraqi government.

Jan. 11: A top Syrian National Council official claimed that discussions are underway with all opposition military forces, including the Islamic Front, to create a “Free National Army” to fight against extremist Islamist rebel groups and the Assad regime. The Islamic Front is reportedly considering the idea, said to involve a complete restructuring of the Free Syrian Army’s Supreme Military Council. Six ISIS fighters were killed in Idlib in clashes with Islamist and rebel battalions. On Jan. 6, a Belgian ISIS emir in Idlib threatened that hundreds of ISIS fighters are ready to carry out suicide car bombings in the province. In Aleppo, two suicide bombers detonated near rebels, the Al Nusrah Front bombed a regime building, and an “infamous” rebel battalion executed a civilian suspected of fighting for ISIS and allegedly raped his mother. Rebels in Homs reported that ISIS killed over 30 Islamist rebel fighters in al-Tiba over the past three days. In Raqqah, ISIS seized the Tal Abyad border crossing into Turkey after fighting with the Islamist movement that had controlled it. In Hama, 12 civilians were killed when rebel battalions bombed their home.

Jan. 12: The ISIS recaptured much of Raqqah city; the Ahrar al Sham did not oppose ISIS. Rebel and Islamist battalions, including one affiliated with Al Nusrah Front, clashed with ISIS in Raqqah. In Aleppo, the ISIS clashed with Islamist battalions in Jarabalus city and at the Bab al-Salama border crossing; ISIS also killed a senior commander in the Mujahideen Army’s Nour al-Din Zanki brigades. State media claimed that security forces in Damascus killed and wounded a number of Islamic Front fighters in Adra and a number of Al Nusrah Front fighters in Madaya. One ISIS foreign fighter was killed in a clash with an Islamist movement in Hasakah. Islamist rebels targeted a regime checkpoint in Deir Izzour. An ISIS car bomb in Idlib killed one rebel. An opposition activist group claimed that some 700 people, including 351 combatants from Islamist and non-Islamist rebel battalions, and 246 ISIS fighters, have been killed fighting each other in the past nine days.

Jan. 13: The ISIS captured al Bab in Aleppo from rebel units, setting up checkpoints and conducting house-to-house searches. State media claimed that security forces killed scores of Islamic Front fighters in Damascus and destroyed a large quantity of weapons and uncovered terrorist tunnels in Aleppo. ISIS and rebels clashed in Aleppo, but ISIS and rebels also fought against regime forces in the province. A car bomb near an Islamist movement checkpoint in Idlib killed at least five rebel fighters. In Homs, Islamist rebels executed three members of Syrian intelligence, and ISIS executed at least 14 rebels after clashes in the desert. In Raqqah, ISIS killed at least 46 members of an Islamist movement who were leaving Raqqah for Hasakah. The Al Nusrah Front said that six brigades in Ghouta have joined it, claimed the killing of 65 Kurdish PKK fighters and regime troops in Hasakah as well as an attack on a Shiite brigade in Damascus, and vowed revenge for the killing of Muslims at Matahen in Homs.

Jan. 14: Regime forces have retaken a number of towns on the outskirts of Aleppo. An ISIS suicide car bombing in Idlib killed at least 13 Islamic movement fighters. ISIS clashed with regime forces near the 17th division base in Raqqah, after the Islamist movement controlling the base withdrew a few days ago. Islamist and rebel battalions in north Reef Aleppo clashed with ISIS and took over two towns.

Jan. 15: The ISIS, the Al Nusrah Front, and Islamic battalion fighters clashed with regime forces in eastern Ghouta in Reef Dimashq, and Al Nusrah and rebels clashed with regime forces near Maaloula. The Kurdish YPG accused the Syrian National Coalition of supporting ISIS against YPG forces in Hasakah. Residents of Hasakah mourned the deaths of 39 YPG fighters killed over the past month by ISIS, Al Nusrah, and Islamist rebels; ISIS and allies have taken over the Qamishli countryside. An ISIS suicide bomb killed at least 26 people in Jarabalus city in Aleppo; ISIS also clashed with Islamic battalion fighters and rebels in the province. In Raqqah, ISIS tortured and killed two Kurdish civilians and set free dozens of Islamist rebels it had captured earlier. In Idlib, Belgian ISIS commander Abu Baraa was killed in Saraqeb, and another non-Syrian ISIS fighter was injured, in an ambush by Islamic fighters; “hundreds” of ISIS fighters are said to be in Saraqeb.

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