The Iraq 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 Iraqis were killed in the first three to four years of conflict. US troops were officially withdrawn in 2011. However, following the spread of the Syrian Civil War and the territorial gains of the Islamic State of Iraq and the Levant (ISIL), the Obama administration decided to redeploy US forces to Iraq in 2014. Many former soldiers are employed by defense contractors and private military companies. 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 as part of the George W. Bush administration’s War on Terror, following the September 11 attacks.