The justification for invading Iraq was a claim that they were developing nuclear weapons. It was well known at the time that the evidence was flimsy, and that even if true it was a flimsy excuse for an invasion. The main piece of evidence was an intercepted shipment of aluminum tubes that were soon shown to have nothing to do with a nuclear program. (See https://en.m.wikipedia.org/wiki/Iraqi_aluminum_tubes). That one is not a conspiracy theory.