Once they were a sideshow to the struggle between Bashar al-Assad’s forces and the rebels battling to oust him. Now, Syria’s Kurdish militants are reshaping battlefronts and putting international alliances to the test.

Following recent advances in northern Aleppo, the Kurdish People’s Protection Units, or YPG, are playing Moscow and Washington against each other and straining relations between the US and its Nato ally Turkey.

Openly backed by the US, indirectly supported by Russia and under attack by Turkey, the YPG have exploited Russia’s military campaign to help Mr Assad, advancing perhaps faster than even regime forces. The Kurdish militants have seized towns from the opposition despite the rebels being backed by the Gulf states, Ankara and their own partner, Washington. […]