(BEIRUT) — U.S.-backed Syrian Kurdish forces captured a strategically important air base from Islamic State militants in north Syria on Sunday in the first major victory for the group since the U.S. airlifted the forces behind enemy lines four days ago. The Kurdish-led Syrian Democratic Forces announced they had captured the Tabqa air base, 28 miles west of Raqqa, the Islamic State group’s de facto capital in Syria. The U.S., which has provided substantial air and ground support to the SDF, ferried hundreds of SDF forces, as well as U.S.