What we have observed since the fall of Baghdad:
More threats of terror worldwide
More innocent lives killed by terrorists (think 3/11)
Al-Qaeda moving into the power vacuum in Iraq
Saddam Hussein's fall from grace
Abu Musab Al-Zarqawi's rise to notoriety
The main events, in short had been Osama bin Laden seeing an opportunity to use Iraq as a new terrorist base since it had fallen into anarchy and was occupied by a hated army (that of the US). Enter Al-Zarqawi following Saddam's capture. Basically, Al-Zarqawi is playing up the sentiments of the disenfranchised Sunnis and turning them over to Osama's cause.
If the US had not decided to take over the oil supply in Iraq, maybe there would be less reason for Al-Qaeda to set their sights on Iraq. Saddam was a dictator indeed, but did he really have any links to terrorist groups? The US intelligence appeared dodgy at times. Hence there was a lack of support from key NATO allies like France and Germany. If you have also noticed, there had been no terrorist attacks on French or German soil for quite a while.