Jack Fairweather's new book argues the war could turn out to be the defining tragedy of the 21st century.
More high-ranking members of the Syrian military are reportedly fleeing into Turkey, and officials there have called an emergency meeting of NATO to discuss the ongoing crisis.
Inside Syria, the violence appears to have escalated with activists claiming more than two hundred people were killed over the weekend in heavy fighting between government forces and rebel fighters.
The BBC’s Ian Pannell spent the last two weeks with some of these groups in Idlib Province in northern Syria.
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