Called "Civil War". As each side demands reprisals, it'll get worse.
Don't see how it can be prevented. Who started what is lost in antiquity, and the politicians on either side has to authorize force or be viewed as "soft on - - - ".
Predicted. Natural outcome of destabilizing Iraq.
By the way, Saddam's violence wasn't for the sake of violence, it was to prevent civil war. Shades of GWB. I know, there are folks who will say that he did it for bloodlust.
He gassed people, with the aid of the US. And the US used "Shock and Awe", white phosporous wrapped around mortar shells to injure people, 500 pound bombs on cities, and other form of terror tactics.
To prevent a civil war.
Arf