The Iraq War, sometimes called the Second Iraq War or the Second Gulf War, and codenamed Operation Iraqi Freedom, 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 1,033,000 Iraqis were killed in the first three to five years of conflict. U.S. troops were officially withdrawn in 2011. The invasion occurred as part of the George W. Bush administration's War on Terror following the September 11 attacks.