If it was done to stop or prevent a civil war that's as good a reason as any. They really must be exterminated,and new means of entry blocked, much as one does to a nest of cockroaches.
It wasn't. There is no civil war in Iraq. There is no imminent civil war in Iraq. Iraq is not "on the brink of a civil war."
That's ALL media hyperbole and they bring the civil war one out, dust it off and take it for a spin every chance they get.
This was NOT done to prevent a civil war because there wasn't one to prevent.