The rebellion against the regime originated in Syria’s civil war that began in 2011. That challenge to his rule, a chapter in the Arab Spring that also convulsed Tunisia and Egypt, led Assad to turn his regime into a police state, with tens of thousands of people jailed and many of them tortured. But the regime never fully secured the northwest of the country. In a matter of weeks, the rebel offensive captured the country’s largest city, Aleppo and the rest of the northwest. Now it controls Damascus. At least three forces appear to comprise the rebellion, with Hayat Tahrir al-Sham (HTS), whose name means Organization for the Liberation of the Levant, the most important.