A major offensive has seen rebel groups in Syria retake the country’s second city, Aleppo – and demonstrated the growing prominence of the Islamist group Hayat Tahrir al-Sham in the 13-year-long civil war.

The World's Host Carolyn Beeler speaks with Martin Smith, the first Western journalist to interview HTS leader Abu Mohammed al-Jolani a few years ago for a Frontline film called "The Jihadist."

Sir Keir noted that while it was 'very good' that Assad was gone, it didn't mean that what follows was settled by any means.

Qaeda, led the offensive against Assad but now faces challenges in governance and legitimacy amidst Syria's long-standing instability.