File - In this Friday, Aug. 17, 2012 file photo, Yemeni volunteers prepare to bury the bodies of unidentified people who were killed during the last year's clashes between government forces and tribal militants at a mass funeral in Sanaa, Yemen.Ten years ago, an uprising in Tunisia opened the way for a wave of popular revolts against authoritarian rulers across the Middle East known as the Arab Spring. For a brief window as leaders fell, it seemed the move toward greater democracy was irreversible. Instead, the region saw its most destructive decade of the modern era. Syria, Yemen, Libya and Iraq have been torn apart by wars, displacement and humanitarian crisis. (AP Photo/Hani Mohammed, File)