The rebel group that led the ouster of Syrian President Bashar al-Assad - Hayat Tahrir al-Sham (HTS) - has long been under United Nations sanctions, which the U.N. special envoy for Syria Geir Pedersen has described as "a complicating factor for all of us.

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.