<Tr> <Td> <Ul> <Li> </Li> <Li> </Li> <Li> </Li> </Ul> </Td> </Tr> <Ul> <Li> </Li> <Li> </Li> <Li> </Li> </Ul> <P> The Iraq War, also known as the Second Gulf War, was a protracted armed conflict that began in 2003 with the invasion of Iraq by a United States - led coalition that overthrew the government of Saddam Hussein . The conflict continued for much of the next decade as an insurgency emerged to oppose the occupying forces and the post-invasion Iraqi government . An estimated 151,000 to 600,000 or more Iraqis were killed in the first 3--4 years of conflict . The U.S. became re-involved in 2014 at the head of a new coalition; the insurgency and many dimensions of the civil armed conflict continue . The invasion occurred under the pretext of a declared war against international terrorism and its sponsors under the administration of US President George W. Bush following the September 11 terror attacks . </P> <P> The invasion began on 20 March 2003, with the U.S., joined by the United Kingdom and several coalition allies, launching a "shock and awe" bombing campaign . Iraqi forces were quickly overwhelmed as U.S. forces swept through the country . The invasion led to the collapse of the Ba'athist government; Saddam was captured during Operation Red Dawn in December of that same year and executed by a military court three years later . However, the power vacuum following Saddam's demise and the mismanagement of the occupation led to widespread sectarian violence between Shias and Sunnis, as well as a lengthy insurgency against U.S. and coalition forces . Many violent insurgent groups were supported by Iran and al - Qaeda in Iraq . The United States responded with a troop surge in 2007 . The winding down of U.S. involvement in Iraq accelerated under President Barack Obama . The U.S. formally withdrew all combat troops from Iraq by December 2011 . </P>

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