The most influential militant group is the Al Qaeda-offshoot Islamic State of Iraq and Levant (Isil), the successor to the Islamic State of Iraq that was formed at the end of 2006. Isil is strongest in Anbar – where it runs training camps in the desert – and retains at least partial presence in Ramadi, Fallujah and Nineveh. In Mosul, Isil functions as the mafia in the city, extorting millions of dollars every month from local businesses.
On account of its vast financial clout, as well as boosts in manpower following the US troops' withdrawal and Baghdad prison breaks in July last year that saw hundreds of prisoners escape, responsibility for the frequent coordinated bomb attacks targeting civilians in Baghdad and elsewhere can be reliably traced to Isil. The group is also the only one among the active insurgent groups capable of targeting points south of Baghdad on an occasional basis, including Kut, Wasit and Nasiriyah governorates. This also applies to the autonomous Kurdish region, which is now dealing with a "blowback" from Iraqi Kurdish recruits to Isil who have headed to Syria.
Isil in Iraq is more openly advertising its operations in Anbar, Nineveh, Salah ad-Din and Diyala provinces on social media. Isil is also attempting to demonstrate institutions of proto-state building in Fallujah, most notably issuing a statement on the establishment of an Islamic virtue and vice committee in the town.
Ideologically, the closest group to Isil is Jamaat Ansar al-Islam (JAI), a 2007 offshoot of the defunct Iraqi Kurdistan Al Qaeda-affiliated Ansar Al Islam. JAI primarily operates in Nineveh, Kirkuk and Salah ad-Din provinces, with occasional operations in Baghdad. But the frequency of operations conducted by JAI nowhere nears that of Isil. While Isil can carry out well over 100 operations in Nineveh in a single month, JAI nationwide manages only a couple or few dozen at most.
Although both groups support the establishment of a caliphate, engage in takfir (accusing Muslims of apostasy) and target Shia civilians, JAI is actually the most notable among the other insurgent groups for its deep rivalry with Isil. This has led to multiple clashes in Kirkuk and Nineveh. One JAI supporter in Mosul told me that Isil had killed 40 JAI members between April and December. In February 2013, JAI appealed to Al Qaeda chief Ayman Al Zawahiri to restrain Isil's conduct.
JAI's key grievance against Isil is that Isil does not consider itself a mere group or faction like others – an important complaint echoed in Syria. Indeed, on jihadi forums, JAI members and supporters were the first to popularise references to Isil as a jamaat, or "group", which is now a standard part of Syrian rebel discourse in refusing to accept Isil' claims to being a state (in turn, JAI circles also now use the Arabic acronym "Daesh", used as a derogatory term, to refer to Isil). This has infuriated Isil circles, who denounce JAI for supposedly not supporting the project of a caliphate and deride JAI's members as criminals.
Apart from these two groups, the most generic term used for the insurgency is "revolutionaries of the tribes". This has entailed the declaration of a number of tribal "military councils", beginning in Anbar and spreading out elsewhere.
The general Anbar tribal military council is the most prominent. It likely comprises a variety of nationalist insurgents from old groups that generally ceased to be active after 2008 or once the US occupation ended, such as the 1920 Revolution Brigades and the Salafi-leaning Islamic Army of Iraq, which following the US withdrawal set up an activist wing called the Sunni Popular Movement which participated in the 2012 protests.
Outside of Anbar, however, it is apparent that a number of these tribal military councils are simply fronts for the Baathist Naqshbandi Army, which distinguishes itself from the other groups in engaging in occasional cross-sectarian messaging. This Naqshbandi influence is most apparent in the social media output released via Intifada Ahrar Al Iraq, the Naqshbandi's activist wing, purporting to show Shia tribal military councils against the government in areas like Karbala.
Besides these so-called tribal military councils, there are also other new generic banners around which insurgents have gathered, most notably the Jaysh Al Izza wa Al Karama ("Army of Pride and Dignity"), reflecting the name of the protest sit-in sites in various areas in which Sunni Arabs gathered last year.
The relations of the other groups with Isil, besides JAI, are complex. One can find evidence of insurgents deriding Isil as Daesh, while Isil circles themselves ultimately distrust the other groups, particularly the Naqshbandi, for supporting supposedly un-Islamic agendas, despite apparent cooperation recently between Isil and the Naqshbandi in seizing three localities in Salah ad-Din province.
On the whole, it seems unlikely that the Iraqi government will be able to revive a widespread "Sahwa" movement, the popular anti-insurgency Awakening Councils in 2005, against Isil for the time being. Meanwhile, killing will likely continue. None of these groups has the strength to dislodge the central government from power, but the government is similarly unable to decisively defeat them. Isil poses the most serious terrorist and military threat, while the other groups primarily constitute a problem for the government to assert control in Sunni Arab areas.