As I understand it, ISIS exists because the Bush-Cheney geniuses dismantled the Iraqi army after that ill-advised...nay criminal..war. As a bonus, they destroyed the existing balance of power in the Middle East since Iraq was a bulwark against Iran. Swell.
Well, Ba’athists are basically Arab Muslim fascists. The defeat of Saddam’s forces and deprecation of Ba’athism in Iraq infuriated many Iraqi Sunnis. Then add to that the imposition of elections which granted (60%) majority to Shia and that was the making of ISIS.
The Iraqi Army just stopped being paid. They went home to de-Ba’athify the organization. Many were re-hired but also a great many Shia were brought into the IA and promoted to leadership positions. This further alienated Sunnis. AIQ/ISIS was mainly ex-IA. Nothing to do with “Bush-Cheney” but what happens when a religious sect and political party which ran a country for 35 years as a military dictatorship is deposed and replaced by their victims. They went nuts.
I don’t worry about Iran much. Bunch of shrinking violets and moronic fanatics. I consider them to be much less harmful than militant Sunnis.