One of the reasons why the United States invaded Iraq in 2003 was because the U.S. believed that Iraq possessed weapons of mass destruction.
The war in Iraq was a conflict that began on Thursday, March 20, 2003 and ended on Sunday, December 18, 2011. After the war ended, a training operation for Iraqi troops to fight the insurgency and the terrorism began.
The main justification for this operation offered by President George W. Bush was the assertion that Iraq possessed and was developing weapons of mass destruction, in violation of a 1991 agreement.
After the invasion, the Iraq Research Group concluded that Iraq had completed its programs to develop such weapons in 1991 and there were none at the time of the invasion, but that they intended to resume production at all times and when the sanctions were lifted.