The Main Combatants
ISIS: The jihadist group, according to my colleague Liz Sly, has a fighting force that is probably larger than the 10,000 or so members estimated in most reports. They are well-armed and have boosted their arsenal after looting equipment from Mosul's main army bases. In every city they overrun, ISIS frees hundreds of prison inmates, some of whom may be like-minded militants.
Reports on Wednesday suggested that ISIS's ranks may have grown after collaboration with militias connected to the old Baathist regime of fallen dictator Saddam Hussein; they played a role in ISIS's reported capture of Tikrit, Hussein's home town. ISIS appears to be well-funded, benefiting from the same shadow networks of donors in the Arab world who funded al-Qaeda as well as the widespread practice of extortion and kidnapping, and other criminal activities.
Iraq's government: The Iraqi army in Mosul wilted in the face of the ISIS assault. Despite billions of dollars spent by the United States in training the post-Hussein army, it suffers from poor organization and morale. The divisive rule of the Shiite-dominated government in Baghdad has, in part, been blamed for the hopeless security situation in the country's Sunni-majority areas.
The units that retreated, shorn of uniforms and much of their armaments, will have to reassemble with reinforcements from Baghdad, but that may be difficult, given the number of battles the government is already fighting with ISIS around towns nearer to the capital. Iraqi helicopters and fighter jets have struck ISIS positions across the country, but the militants are still reportedly advancing closer to Baghdad. Powerful Shiite cleric Moqtada al-Sadr has called for the mustering of Shiite militias to operate in the vacuum. This gives the conflict an even more dangerous and sectarian edge, something the Sunni extremists in ISIS probably hoped to achieve.
Kurds: The autonomous government in the Iraqi region of Kurdistan has rallied its own forces, known as the pesh merga, to combat ISIS. Although the Kurds have had an adversarial relationship with Baghdad for quite some time, reports suggest they are now more closely coordinating efforts to counter ISIS. The pesh merga have long eyed Mosul, which has a significant Kurdish population and lucrative oil fields. They possess some light armored vehicles as well as artillery and will probably be the key to winning back Mosul. That, as the Checkpoint blog notes, could in the long run lead to renewed Kurdish claims and further tensions with Baghdad.
Turkey: ISIS has reportedly captured several Turkish diplomats, as well as other Turks, in Mosul. It raises fears of a growing regional conflagration. Turkey is in an awkward position: ISIS fighters in Syria have routinely wound up in hospitals in Turkish border towns, rumored to be tolerated by Ankara because of their own battles with Kurdish militias in Syria. Renewed protests and unrest in Kurdish towns in Turkey make the situation all the more delicate.
Iran: The Shiite state will look upon developments in Iraq with great concern. ISIS is a real foe, and its success in Syria and Iraq is an existential challenge to two staunch allies of Tehran. Iran's foreign minister on Wednesday promised Baghdad support in its fight against "terrorism." Iranian aid may be seen most conspicuously in the emboldened Shiite militias that could spring up to counter ISIS.
U.S.: The State Department deemed the situation in Iraq "extremely serious" and has recently provided 300 Hellfire missiles, small arms and tank ammunition, helicopter-fired rockets, machine guns and rifles to the Maliki government. This is on top of the billions of dollars spent training the Iraqi army in the wake of the 2011 U.S. withdrawal from Iraq. It remains to be seen what kind of action the United States would contemplate should the situation get even worse. A robust military response would raise questions about why the United States did not act similarly in neighboring Syria. It would also awkwardly place Washington in the same camp as Tehran. For now, U.S. officials are calling for political and ethnic reconciliation within Iraq, a long-standing refrain that has had little effect for the past decade.