well, the precursor to ISIS (Al Quaida) is what rose up but I agree with your point. Hindsight being 20/20, we should not had invaded but he was a totalitarian despot who had absolutely used WMDs against the Iranians and his own people and there was a concern he would provide those WMDs to terrorists. AQIZ (Al Quaida in Iraq) was actually transitioning into a political party as we pulled out. ISIS formed in Syria and has been partially attributed to Obama's policies and their support for anti-Assad forces. ISIS' ability to take land in Iraq (Tal Afar and Mosul, then down the river) is because the new Iraqi army was not fully trained when we left (which is what we were doing when we left - training them).
I agree that had we not invaded none of this would be happening, but we don't know what else might have happened.