"Weeks away from retirement, Army Chief of Staff Gen. Ray Odierno believes that the U.S. military could have thwarted the rise of the Islamic State (IS, also known as ISIS or ISIL) had the Obama administration left troops in Iraq beyond 2011.-Morgan Chalfant
...the top Army officer, who has spent 39 years in the military and spent more time in Iraq than any other U.S. general, labeled the rise of IS “frustrating to watch,” suggesting that it was a mistake for the United States to pull out of the region at the end of 2011.
I go back to the work we did in 2007, 2008, 2009, and 2010 and we got it to a place that was really good,” Odierno detailed. “Violence was low, the economy was growing, politics looked like it was heading in the right direction.”
If we had stayed a little more engaged, I think maybe it might have been prevented,” he supposed, adding later that “it would have been good for us to stay” after the end of 2011. Though he had recommended in 2009 that the United States keep 30,000-35,000 troops in Iraq beyond 2011, his recommendation was rejected."