Congress and the people of this nation were told we were in imminent danger of attack by Iraq's chemical and WMDs.
Danger was so imminent we could not allow UN Inspections to complete or form a truly unified coalition against Iraq. The U.S., being strong of will and righteous in our quest, would go it alone against the looming forces of evil.
So, Bush formed a weak/symbolic alliance, preemptively invaded Iraq, alienated the UN and significant multinational supporters, deeply divided our nation, depleted our budget surplus and created the largest budget deficit in our history; only to find there were no WMDs or imminent danger. If Bush weren't so arrogant, took time to gather information and built an effective collation we could have saved thousands of lives, enjoyed world support, spent our billions securing our own shores, educating our own children, providing heath care to our nation, maybe even found Bin Laden and crippled Al Qaida (who attacked us 9-11, not Iraq).