How Syria’s rebels launched a surprise offensive to retake Aleppo

How has a Syrian rebel lightning offensive managed to seize Aleppo from Bashar al-Assad's regime? Who are the leaders, Islamist group Hayat Tahrir al-Sham? And could it reignite the civil war? Venetia Rainey is joined by Dr Haid Haid, Syrian columnist and consulting fellow at Chatham House, to…