Charles Lister is a resident fellow at the Middle East Institute and a senior consultant to the Shaikh Group’s Syria Track II Initiative. He is the author of "The Syrian Jihad: Al-Qaeda, the Islamic State and the Evolution of an Insurgency," and is on Twitter.

In the past week, the Syrian crisis has spiraled out of control, largely due to fundamental U.S. misjudgments over the strategic calculations and ambitions of Russia, Turkey, the Syrian opposition and the main Kurdish force in Syria, the Y.P.G.

Otherwise, Russia will build on its relationship with Kurdish forces, undermining the United States and creating another intractable conflict.

It was entirely predictable that the Pentagon’s favored anti-ISIS partners — the Y.P.G.-dominated Syrian Democratic Forces — would one day turn their guns on the C.I.A.-backed Free Syrian Army in pursuit of their own territorial aims. That they have done so under Russian air cover rubbed salt in an already raw wound. Similarly inevitable then, was Turkey’s intervention against what it perceived as the imminent establishment of a state ruled by the Kurdish-separatist party, the P.K.K., along its already unstable southern border.

Despite its mistakes, the U.S. and its partner states must strongly encourage de-escalation. Since downing a Russian jet in November, Turkey has frequently demonstrated insufficient restraint in dealing with tensions on its borders. But the United States must also acknowledge Ankara’s legitimate security concerns. After all, 49 Turkish security forces and civil servants were killed by the P.K.K. and a splinter faction of the P.K.K. between Feb. 16 and 21 alone.

As it faces and contributes to intensifying fighting with the P.K.K., Turkey has been made to watch the U.S. government embolden the Y.P.G. — the P.K.K.’s Syrian wing — to an extent that it could probably never have imagined. As a NATO ally, Turkey has a right to question U.S. actions.

The Y.P.G. explicitly stated its allegiance to the P.K.K. — which the U.S. State Department has considered a designated terrorist organization since 1997 — within its internal code until last year, when that text was removed. Interestingly, the U.S. National Counterterrorism Center also labelled the Y.P.G. as the P.K.K.’s “Syrian affiliate” until last year, by which time it had become a partner in the fight against ISIS.

The U.S. must also aggressively demand that the Y.P.G. cease its attacks on the Syrian opposition. Should they continue, we will have allowed the eruption of a conflict in Syria potentially as intractable as the one now raging between the opposition and Assad regime. Thus far, weak calls for the Y.P.G. to “show restraint” from its “counterproductive” behavior only encourage Russia to build on its own growing relationship with the Y.P.G. to further undermine the United States.

More broadly, Syria’s "Kurdish issue" deserves a heightened position on the international agenda. While Kurds were consistently denied their rights by the Assad regime, Syria’s opposition strongly rejects ethnic discrimination and includes within it many Kurds who are not members of the Y.P.G.

Today’s hostilities are the result of intense suspicion between the Y.P.G. and the Syrian opposition over each others ambitions for Syria’s future. Bridging these psychological walls may be the only way of ensuring that a successful fight against ISIS ends in anything but continued intramilitia warfare.



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