The Iraq War was a protracted armed conflict in Iraq from 2003 to 2011 that began with the invasion of Iraq by the United States-led coalition which overthrew the Iraqi government of Saddam Hussein. The conflict continued for much of the next decade as an insurgency emerged to oppose the coalition forces and the post-invasion Iraqi government. US troops were officially withdrawn in 2011. The United States became re-involved in 2014 at the head of a new coalition, and the insurgency and many dimensions of the armed conflict continue today. The invasion occurred as part of the George W. Bush administration's War on Terror following the September 11 attacks.
In October 2002, Congress granted President Bush the power to decide whether to launch any military attack in Iraq. The Iraq War began on 20 March 2003, when the US, joined by the UK, Australia, and Poland launched a "shock and awe" bombing campaign. Iraqi forces were quickly overwhelmed as coalition forces swept through the country. The invasion led to the collapse of the Ba'athist government; Saddam Hussein was captured during Operation Red Dawn in December of that same year and executed three years later. The power vacuum following Saddam's demise and mismanagement by the Coalition Provisional Authority led to widespread civil war between Shias and Sunnis, as well as a lengthy insurgency against coalition forces. The United States responded with a build-up of 170,000 troops in 2007. This build-up gave greater control to Iraq's government and military and was judged a success by many. In 2008, President Bush agreed to a withdrawal of all US combat troops from Iraq. The withdrawal was completed under President Barack Obama in December 2011. Wikipedia