Syrian rebel forces led by Hayat Tahrir al-Sham, or HTS, declared they had ousted President Bashar al-Assad and he had fled Damascus on Sunday. But what is HTS, and how did it rock the long-simmering tensions in Syria? HTS is a Sunni Islamist militant and political group that traces its roots to the beginning of the Syrian civil war.

Standing before a cheering crowd in Damascus’ historic Umayyad Mosque, the broad and bearded Abu Mohammad al-Jolani declared a new chapter in Syria’s history.