Who are the foreign fighters taking on the Islamic State?

Before supper in their barracks every evening, Sunni Muslim soldiers of the YPG militia, sworn enemies of the Islamic State (Isil), pause while an American born-again Christian says his prayers. Once Jordan Matson has finished saying his one-man grace, the hardened fighting force of Syrian Kurds, now famed for their victory in Kobane, their women warriors and the rescue of the Yazidis from atop Mount Sinjar last summer, tuck in. As night falls, they head out to their trenches and outposts, taking turns on guard duty with other foreigners like Matson, watching for any movement from the jihadists’ lines beyond.