A Who's Who of the Combatants in Iraq

Iraq's Insurgents and Militias

The Sunni Insurgency

Nationalists and Ba'athists — By far the largest category of Sunni insurgents are those that regard themselves as an Iraqi "nationalist resistance" against U.S. occupation. There are scores of such groups, made up mainly of Saddam loyalists and former soldiers. Although the nationalists regard the jihadis with suspicion, they sometimes work together on large operations. The largest nationalist group, Jaish al-Islam, or Army of Islam, has tens of thousands of fighters; others have no more than a few dozen. Their signature form of attack has been the ambushing of U.S. troops using improvised explosive devices (IEDs), but some of these groups have been drawn into sectarian fighting. Jaish al-Islam at one point called on all Sunnis to fight the "battle of destiny" against Shi'ites for control of Baghdad.

Al-Qaeda in Iraq — Founded by Abu Musab al-Zarqawi, the group claims to have more than 3,000 fighters, many of them from countries such as Saudi Arabia, Egypt, Sudan and al-Zarqawi's native Jordan. Its ultimate aim is to set up a worldwide Islamic state. After starting out with kidnappings and videotaped beheadings of captives, the group has evolved into a formidable fighting force. It is responsible for the majority of suicide operations across Iraq. It was the first Sunni group to target Shi'ites for killing; indeed, al-Qaeda is often accused of fomenting the sectarian war. Al-Zarqawi was killed in a U.S. raid in June of 2006. Earlier that year, al-Qaeda in Iraq claimed to have established a Mujahedeen Shura Council with five Iraqi jihadist groups. The move was likely a response to some insurgent groups questioning whether al-Qaeda, run by foreign fighters, had a legitimate role in the Iraqi resistance. By most accounts, al-Qaeda completely dominates the group, using it merely as a rubber stamp.

Ansar al-Isam — Also known as Ansar al-Sunnah, this jihadi group is based in the mountains of northern Iraq but is able to conduct operations as far south as Baghdad. It often works closely with al-Qaeda in Iraq and employs similar techniques, such as suicide bombing. Its alleged leader, Mullah Krekar, lives in Norway, where he is deemed a refugee. The U.S. alleges that Ansar al-Islam receives support from Iran.

Shi'ite Militias

Mahdi Army — These black-clad militiamen, loyal to the radical cleric Moqtada al-Sadr, are blamed for most of the sectarian killings following the bombing of the Shi'ite Golden Mosque shrine in Samarra in 2006. Their stronghold is the vast Baghdad slum of Sadr City, home of 2.5 million mostly impoverished Shi'ites. The Mahdi Army has several smaller units that don't always answer to al-Sadr — the U.S. military describes them as "rogue militias" — but continue to fight in his name. The army began as a rag-tag group that sprang into existence in the summer of 2003, after the fall of Saddam Hussein. U.S. forces were able to crush its attempted insurrection in Najaf in 2004, killing hundreds of its fighters. But as al-Sadr gained political strength, the militia grew in size, financial resources and military sophistication. There are now thought to be tens of thousands of Mahdi Army fighters. Many have infiltrated the Iraqi security forces, especially the police.

Badr Organization — Formerly known as the Badr Brigade, this militia is the armed wing of the Supreme Council for the Islamic Revolution in Iraq, or SCIRI, the country's largest Shi'ite political party. Many of its fighters were recruited and trained in Iran during the Saddam era, and carried out small guerilla operations against his regime. Since Saddam's fall, a number of them have been absorbed into the Iraqi security forces. But many remain involved in the militia, which is better organized and disciplined than the Mahdi Army but not as numerous. The Badr Organization's leader, Hadi al-Amiri, is a member of parliament. Badr and Mahdi army forces have clashed periodically in turf battles.

Kurdish Peshmerga

Kurdish fighters loyal to the the Kurdistan Democratic Party of Massoud Barzani and the Patriotic Union of Kurdistan of Jalal Talabani (currently Iraq's president) who spent decades fighting a guerrilla war against Saddam Hussein's regime are collectively known as the "Peshmerga," (translated as "those who face death.") Having helped the U.S. topple Saddam, the Peshmerga were quickly given security responsibility for the Kurdish areas of northern Iraq and eventually absorbed, en bloc, into the Iraqi government's security forces. Although they have periodically been deployed elsewhere in Iraq in support of U.S. troops, their primary responsibility remains protecting the Kurdish areas of northern Iraq, as the security force of the Kurdistan Regional Government. The Peshmerga are estimated to keep around 100,000 men under arms, and other, non-Kurdish units of the Iraqi security forces are barred from entering Kurdish areas.

—Aparisim Ghosh/Baghdad