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.

Russia has conducted major air strikes on rebels in Syria after insurgents led by the Islamist Hayat Tahrir al-Sham group swept into Aleppo in what is the biggest challenge to its ally President Bashar al-Assad in years.

Turkey could be one of the big winners from the new Syria crisis, giving it a chance to tackle its Syrian refugee problem and the Kurdish threat along its border, observers say. Although Syrian President Bashar al-Assad spurned an offer of help from his Turkish counterpart Recep Tayyip Erdogan,