November 1998, at the urging of President Bill Clinton, the U.S. House of Representatives and the US Senate passed the "Iraq Liberation Act of 1998, which "declare[d] that it should be the policy of the United States to remove the Saddam Hussein regime from power in Iraq and to replace it with a democratic government."
On October 16, 2002 an Authorization for Use of Military Force Against Iraq Resolution of 2002 was passed in the United States House of Congress.
In November, 2002, UN Security Council Resolution 1441 was passed unanimously demanding that Iraq comply with its disarmament obligations as well as previous resolutions on human rights, terrorism and prisoners of war.
Beginning with a speech to the United Nations General Assembly on September 12, 2002 President George W. Bush began a public campaign to convince the world that Saddam Hussein was violating both the commitments he had made at the end of the First Gulf War and which prior UN resolutions dealt with: weapons of mass destruction, human rights, Kuwaiti prisoners of war, terrorism, long range SCUD missiles, the U.N. Oil-for-Food Programme and allowing UN inspectors to return to Iraq after their removal in 1998
On October 10, 2002 the 107th Congress of the United States passed HJ Res 114 titled "Authorization for Use of Military Force Against Iraq Resolution of 2002." Among the reasons noted in the Congressional resolution authorizing force were, Iraq's non-compliance with U.N. Security Council Resolution 1441, aid to terrorists (PALF), a 1993 assassination attempt on former President George H. W. Bush (George W. Bush's father)and the Emir of Kuwait, in addition to violations of the no-fly zones.
In a January 27, 2003 report to the U.N., chief inspector Hans Blix, while noting Iraqi cooperation with regards to prompt access to inspection sites, stated "...Iraq appears not to have come to a genuine acceptance, not even today, of the disarmament which was demanded of it and which it needs to carry out to win the confidence of the world and to live in peace." The reasons for this include a failure to account for quantities of VX nerve agent and anthrax and also the inability of the U.N. to interview Iraqi scientists outside the country.
On February 5, 2003 Colin Powell attempted to convince the UN Security Council of the threat Saddam Hussein's regime posed.
The Bush administration also claimed that Iraq had ties to al Qaeda and other terrorists organizations, including the Palestinian Arab Liberation Front (PALF), HAMAS, Islamic Jihad, and Hezbollah. Bush administration officials also claimed that Iraq was reconstituting their development of nuclear weapons.
This site also has some explanations and some interesting info on ties to al-qaeda that were not explained in the senate report last week.
http://www.reasons-for-war-with-iraq.info/