“An island of stability in the midst of the Iraq inferno”—thus wrote Ilnur Çevik, a journalist at Turkey’s pro-government Daily Sabah, about the Kurdistan Region of Iraq when President Masoud Barzani visited Ankara in December. For the first time, Turkey placed Kurdistan’s flag alongside Turkey’s own, a gesture underscoring the countries’ strategic bond. While the Turks hosted Barzani, the Saudis finalized the historic Syrian opposition meeting in Riyadh. The mid-December gathering of political and militant organizations worked to craft common purpose in the Syrian civil war. Yet despite administering Syria’s northeast and fighting grittily against ISIS’ westward sweep, the...