The csuse was Obama and Hillary’s policy
The 2007 Dem-controlled Congress cut the 2008 OCO funding for Iraq and Afghanistan in the 2008 budget. Existing programs were cut to make up the short fall. F-22s were cut. With OCO funding cut, along with a lack of decent SOFA the withdrawal was pre-ordained. Without US forces Iraqi politics and inertia took charge (read: corruption and infighting).
ISIS, aka Al Qaeda-in-Iraq (AIQ), aka Sunni Insurgents, aka Ba’athist Sunnis used their basis of operation in Syria to re-enter Iraq.
After US forces departed Iraq Assad ordered AIQ out of Syria where they had a safe haven since 2005. AIQ refused and began attacking Syrian forces. AIQ’s two-front war against both governments resulted in their re-branding as Islamic State of Iraq and Syria (ISIS).
It is Pelosi, Reed and the rest of the 2007 Democrat Congress which created ISIS.