Here's the deal: 1) Bush did get us into a war in Iraq that we shouldn't have gotten into; 2) in 2008/2009 when Bush left office and mostly because of the 2007 surge, the Sunni Islamic terrorists groups like Al Qaeda in Iraq were relatively powerless in Iraq, and Obama and Biden recognized that; 3) In 2007 Bush encouraged the next President, whoever he or she was, to leave an American military force in Iraq, and the suggestion was about 30,000 troops, and that this would be part of the renegotiation of the Status of Forces agreement that the next President would work out; 4) Obama ran on getting all U.S. military out of Iraq and vowed to keep that promise; 5) when Obama renegotiated the Status of Forces agreement it was for a much smaller force of about 5000 troops with a maximum of 10 thousand; 6) Critics say that this much smaller number gave Prime Minister Nouri Al-Maliki no leverage with members of the council to give American troops immunity; 7) Obama said he couldn't leave any troops in Iraq because of the lack of immunity; 8) Within weeks of the American pullout Al-Qaeda in Iraq/ISIL began attacking the Iraqi government and Shiites, and this continues to today.

So basically Bush shouldn't have sent us to Iraq in the first place and it's possible that if Obama had offered 30,000 troops then immunity would have been granted and ISIS would not have become the monster that it is today. It's not one or the other is true, both are true.

Also, even if ISIS was clamped down on in 2011, it doesn't mean it wouldn't have eventually happened. We, the United States, didn't create Boku Haram in Nigeria, which is an ISIS group. All of these groups came out of the Muslim Brotherhood, which was created in the 1920s. Hamas, Al Qaeda, Boku Haram and ISIS all derive from the MB. They exist in all continents.