The YPG has been the primary ally of the United States in its mission to smash the so-called Islamic State. That mission is now mostly complete, and Secretary of State Rex Tillerson has said the United States will shift gears to focus on stabilizing former Islamic State areas now under YPG control, including by training Kurdish security forces.
Turkish President Recep Tayyip Erdogan didn’t take kindly to this news, accusing the U.S. of building a PKK “terror army” on Turkey’s southern border. America’s strategic recommitment to the Kurds seems to have been one reason for the sudden rush to war.
Erdogan’s choice of Afrin was simple: It is the only YPG-held area not protected by the U.S. Air Force. Due to the political geography of northwestern Syria, Kurdish forces in Afrin haven’t primarily fought the Islamic State. Instead, they mainly faced Turkish- and American-backed rebels vying for control of the border region north of Aleppo. For the U.S. to give air support in Afrin would have meant being drawn into a “proxy war with itself.”