The correct items from the choices listed in the comment box:
A) Bush believed Hussein and Iraq had WMDs.
B) Bush argued that Iraq had previously supported terrorist organizations.
C) The United States claimed that Iraq was not fully cooperating with UN weapons inspectors.
In addition to those overtly stated reasons for initiating war against Iraq in 2003, there was also the underlying "Bush Doctrine" of the value of a "preemptive strike" against a dangerous regime. The Bush Doctrine (after Pres. George W. Bush) proposed that the best defense against terrorism was to use American power to spread democratic values in countries that were potential breeding grounds for terrorist activity.
This sort of policy agenda was part of the "neoconservative" view of a number of President George W. Bush's advisers -- especially some who had also served in the administration of his father, President George H.W. Bush. In the wake of the 9/11 attacks, there was a desire to push American values and not be shy about doing so with the use of American military might. The core ideas of the "Bush Doctrine" were that the United States could pursue this goals on its own (without need for United Nations partnerships), that preemptive strikes were allowable against countries that harbored terrorists, and that regime change for the sake of promoting democracy was a good strategy.