A photo from March 2008 provided by the Hennepin County, Minn., Sheriff's Office shows Douglas McAuthur McCain, who was killed recently fighting alongside Islamic State militants in Syria. AP hide caption

itoggle caption AP

American Eric Harroun threatened Bashar Assad on Facebook and YouTube. He spent six weeks fighting with a rebel army, a journey that did not end well for him. ABC News/YouTube hide caption

itoggle caption ABC News/YouTube

Secretary of Defense Chuck Hagel (left) and Chairman of the Joint Chiefs of Staff Gen. Martin Dempsey during a Pentagon briefing on Thursday. Hagel said Islamic State militants in Iraq and Syria posed a threat "beyond anything we've seen." Yuri Gripas/Reuters/Landov hide caption

itoggle caption Yuri Gripas/Reuters/Landov

Syrians inspect a site hit by what they said were airstrikes carried out by President Bashar Assad in the Eastern Ghouta area on Aug. 3. Assad's forces continue to besiege the area near Damascus, which is still controlled by rebels. Badra Mamet/Reuters/Landov hide caption

itoggle caption Badra Mamet/Reuters/Landov

President Obama leaves after making a statement Wednesday about the killing of journalist James Foley in Syria. The president said the U.S. would continue to confront Islamic State extremists despite the brutal murder. Jacquelyn Martin/AP hide caption

itoggle caption Jacquelyn Martin/AP

Forces loyal to Syria's President Bashar Assad walk along a street in Mleiha, near the Damascus airport, during a tour organized by the Syrian government on Aug. 15. Omar Sanadiki/Reuters/Landov hide caption

itoggle caption Omar Sanadiki/Reuters/Landov