Iraqis shop for food in preparation for the Muslim fasting month of Ramadan in Baghdad on Saturday. Karim Kadim/AP hide caption

itoggle caption Karim Kadim/AP

A decade ago, U.S. soldiers were fighting and rebuilding in the Iraqi cities of Mosul and Tikrit. The past few weeks have seen those cities, among others, fall to the Sunni militant group ISIS. Here, a member of the Kurdish Peshmerga forces stands guard Thursday near an ISIS checkpoint in Mosul. Karim Sahib/AFP/Getty Images hide caption

itoggle caption Karim Sahib/AFP/Getty Images

This image posted on a militant website shows ISIS fighters marching in Raqqa, Syria, where the extremist group trains recruits, including Westerners. AP hide caption

itoggle caption AP

Joint Chiefs Chairman Gen. Martin Dempsey speaks during a news conference at the Pentagon in December. Manuel Balce Ceneta/AP hide caption

itoggle caption Manuel Balce Ceneta/AP