As Iraq edges toward civil war, here's a look at major players and groups in the crisis.
The Islamic State of Iraq and the Levant (ISIL) is a Sunni jihadist group that has its roots in the al-Qaeda-linked insurgents that formed the backbone of the resistance against U.S. forces in Iraq after the 2003 invasion. It has since expanded operations into Syria, where it is fighting the regime of Bashar Assad, and has broken formal ties with al-Qaeda. It embraces a radical form of Islam and consists of battle-hardened fighters.
Earlier this year, the group ransacked Fallujah and Ramadi, two influential Sunni cities in western Iraq. It has managed to hold much of Fallujah and portions of Ramadi. More recently it seized parts of Mosul and was positioned to edge toward Baghdad.
ISIL is also referred to as the Islamic State of Iraq and Syria (ISIS).
The prime minister of Iraq leads a Shiite dominated government that has alienated many of the Sunnis in Iraq over the past several years. Maliki has been criticized for not taking more steps to include rival Sunni leaders in his government.
Shiites are the majority sect in Iraq, but for most of Iraq's history they were oppressed by the Sunnis, who dominated the government. Saddam Hussein and his key leaders were all Sunnis. Shiite leaders during that time were driven into exile.
Iraq's armed forces
Organized, trained and, to some extent, equipped by the United States, the Iraqi military was a competent force when the United States pulled all its forces out in 2011.
But over the past several years Maliki has been accused of appointing political cronies to key leadership positions and the military has ceased to conduct regular training. Sunnis have said the army is little more than another Shiite militia and have little confidence in its ability to protect them. Many units simply collapsed when insurgents attacked Mosul and other cities in Iraq.
During the U.S. occupation of Iraq, Shiite militias, some of which were backed by Iran, grew to become powerful forces. Among the strongest such militias is the Mahdi Army, a group loyal to anti-American cleric Muqtada al-Sadr.
Shiite militias at various times attacked U.S. forces and also participated in sectarian warfare in Iraq between Sunnis and Shiites, which peaked in 2006. Most of the insurgent gains were in Sunni or mixed areas. Shiite militias will likely try to protect Shiite neighborhoods if insurgents attempt to move into Baghdad.