The surprise offensive on Aleppo by Syrian rebel groups has left the US in the difficult position of not fully supporting either side while also maintaining a force posture of nearly 1,000 troops in Syria as part of the ongoing mission to fight ISIS.

Syria’s devastating civil war, responsible for more than 300,000 deaths, was never officially resolved. Lightning gains by rebels opposed to President Bashar al-Assad were opportunistic, but also indicated years of patient preparations.

In just a few days, a patchwork of rebel forces has seized control of a broad stretch of land in the west and northwest of Syria. But it’s unclear just how much support Syria’s weakened allies can provide.