And ultimately, Saddam was taken in by his own lies.
Misled by Saddam, the Bush administration (and most of the world) honestly believed that he had WMD, and the invasion therefore made sense. So, don't blame Bush for an "unnecessary war."
Blame the lying thug who provoked it.
Like most fascists, Saddam simply wasn't prepared to have his bluff called, despite the astronomic stakes involved.