Syria is once again on the boil. The supposed stalemate of the decade-long civil war was broken last week by a rebel coalition. Until recently, the forces of the authoritarian president Bashar al-Assad controlled most parts of the country. But the situation has changed now. In a matter of days, the anti-Assad forces have made significant territorial gains. They have captured Syria's biggest city Aleppo, entered the key strategic city of Hama and are closing in on Homs and the capital Damascus. Another major blow came today as Daraa, widely regarded as the cradle of Syria's 2011 civil uprising, also took a fall. The regime of Bashar al-Assad stands threatened. Why is this happening?