ISIS became a force when GWB disbanded the Iraqi military. That’s an interesting hypothesis.
I say ISIS became a force when Obama decided to over throw Assad in Syria. He along with McCain were funding the rebels including ISIS.
ISIS grew from the occupation era prisons where Islamic fanatics and Saddam’s military and intel professionals met and bonded in mutual hatred of the US and the West. The disbanding of Saddam’s military and intel agencies was a mistake. For continued salaries and a military honorific in retirement, most would have switched allegience or at least remained inactive in order to keep feeding their families and preserve their status.
I was told basically the same thing by a native Jordanian I work with about seven years ago when we were discussing the Obama/Clinton gang mucking up the Mid East situation. He said the ISIS core was a bunch of muy pissed off former Republican Guards who made the cut post-Saddam.