"Iraq's sectarian and ethnic divisions--muted toward the end of the 2003-2011 U.S. military intervention in Iraq--have reemerged to fuel a major challenge to Iraq's stability and to U.S. policy in Iraq and the broader Middle East region. The resentment of Iraq's Sunni Arabs toward the Shiite-dominated central government facilitated the capture in 2014 of nearly one-third of Iraqi territory by the Sunni Islamist extremist group called the Islamic State (also known as the Islamic State of Iraq and the Levant, or ISIL). Iraq's Kurds have been separately embroiled in political and territorial disputes with Baghdad, although those differences have been at least temporarily subordinated to the common struggle against the Islamic State. […] This report provides background and analysis on the politics of Iraq, including its communities, its governing personalities and factions, security forces and militias, and the government's human rights record. The report does not provide a detailed analysis of the U.S.-led campaign to defeat Islamic State forces in Iraq."
CRS Report for Congress, RS21968
Federation of American Scientists: http://www.fas.org/sgp/crs/index.html