However , the power vacuum following Saddam 's demise and the mismanagement of the occupation led to Causation widespread Dispersal sectarian violence between Shias and Sunnis , as well as a lengthy insurgency against U.S. and coalition forces .

Al-Qaeda 's Iraqi affiliate said Statement on Friday it was behind car bombings Attack against Shias in Baghdad this week that killed Killing 64 people , saying Statement they were revenge Revenge for `` insults Judgment_communication '' and threatening Warning more attacks Attack .

Religious tensions between Sunnis and Shias remained Presence after the war Military_operation .