Free Syrian Army fighters run behind sandbags in Daraa Al-Mahata, in southern Syria, on Jan. 21. Many moderate rebels joined the uprising to fight against President Bashar Assad, but the U.S. plans to train them to fight the self-proclaimed Islamic State. Wsam Almokdad/Reuters/Landov hide caption

itoggle caption Wsam Almokdad/Reuters/Landov

Demonstrators wave Syrian opposition flags during a protest in Istanbul against the government of Syria's President Bashar Assad, on March 15. Osman Orsal/Reuters /Landov hide caption

itoggle caption Osman Orsal/Reuters /Landov

Syrians carry a large revolution flag and chant slogans during a protest in Aleppo, Syria, where young people and children sang songs against President Bashar Assad and the Syrian regime, Dec. 21, 2012. Virginie Nguyen Hoang/AP hide caption

itoggle caption Virginie Nguyen Hoang/AP