Comments by Secretary of State Antony Blinken this weekend were the first time a U.S. official has acknowledged contact with the Syrian rebel group that drove Bashar al-Assad from power.

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 ...