The retaking of Aleppo marks the first major development in years in Syria's grinding civil war, which had largely fallen from the world's headlines. It also raises fresh questions about the opposing sides,

Airstrikes also hit residential buildings in the city of Idlib, which has become a refuge for people displaced by the civil war, killing at least 12 civilians, according to the White Helmets, an independent rescue organization.

Islamist rebel group Hayat Tahrir al-Sham launched a lightning assault against pro-Assad forces in Aleppo. Here’s who else is fighting in Syria’s civil war.