What theory was used to justify US invasion?

The U.S. invasion of Iraq in 2003 was primarily justified through the application of the "Bush Doctrine," which emphasized preemptive strikes against perceived threats. The administration argued that Iraq possessed weapons of mass destruction (WMDs) and had ties to terrorist groups, particularly al-Qaeda, which posed a significant threat to U.S. national security. Despite extensive claims, the subsequent lack of evidence for WMDs led to widespread criticism and debate regarding the legitimacy of the invasion.