For me, the answer to the why of the Iraq invasion rests with this CBS 60 Minutes interview with FBI Agent, George Piro, who interrogated Saddam Hussein for several !onths after he was caught by US and coalition forces.
According to Piro, Saddam led the entire world to believe he had weapons of mass destruction with the hope that Iraq's neighbor, Iran, Saddam's ten year long mortal enemy in a war which cost 1,000,000 lives, would refrain from attacking Iraq after the warring had stopped.
To keep Iran from attacking, Saddam had to make EVERYONE believe he had WMD's.
America could not take the chance that Saddam was bluffing.