"Following the completion of the U.S. withdrawal from Iraq on December 18, 2011, relations among major political factions worsened substantially, threatening Iraq's stability and the legacy of the U.S. intervention in Iraq. After extensive sectarian conflict during 2006-2008, and with U.S. troops still present, Iraq's political system evolved into relatively peaceful political competition and formation of cross-sectarian alliances. Sunni Arabs, always fearful that Prime Minister Nuri al-Maliki would seek unchallenged power for Shiite factions allied with him, accused him of an outright power grab as he sought to purge the two highest ranking Sunni Arabs from government (a deputy President and deputy Prime Minister). The Sunnis have sought to enlist the help of the Kurds to curb Maliki's perceived ambitions; the Kurds also distrust Maliki over territorial, political, and economic issues. The apparent unraveling of the political consensus has created conditions under which the insurgency that hampered U.S. policy during 2004-2008 continues to conduct occasional high casualty attacks, including over a dozen near-simultaneous bombings on December 22, 2011, and several since then."
CRS Report for Congress, RS21968