The 2003 invasion of Iraq, termed "Operation Iraqi Freedom" by the US administration, began on March 20. The United States and Britain supplied 98% of the invading forces. Other nations also participated due to U.S. president George W. Bush's efforts to build a coalition to help with the operation. The 2003 Iraq invasion marked the beginning of what is commonly referred to as the Iraq War. Prior to the invasion, the United States' official position was that Iraq illegally possessed "weapons of mass destruction" in violation of UN Security Council Resolution 1441 and had to be disarmed by force. Bush repeatedly asserted that these weapons posed a grave and imminent threat to the United States and its allies. UN inspection teams were searching Iraq for these alleged weapons for nearly four months prior to the invasion and were willing to continue, but were forced out by the onset of war in spite of their requests for more time. The Bush administration failed to get a U.N. endorsement for war against Iraq on March 17, 2003 and began the invasion on March 20, 2003, which is seen by many as a violation of international law, breaking the UN Charter (see Legitimacy of the 2003 invasion of Iraq. The Iraqi Military was defeated, and Baghdad fell on April 9, 2003. On May 1, 2003, U.S. President George W. Bush declared the end of major combat operations, terminating the Ba'ath Party's rule and removing Iraqi President Saddam Hussein from office. Coalition forces ultimately captured Saddam Hussein on December 13, 2003.

Extensive inspections after Iraq's invasion failed to find substantial proof of weapons of mass destruction. This has once more brought the various already controversial justifications for the invasion into dispute. Post-invasion Iraq has experienced violence from warring sects and an Iraqi insurgency. Numerous terrorist groups have become active in the area. Elections were held in January 2005.
As of 16 September 2008 the US deaths stands at 4158.