To preserve its relations with both Ankara and Rojava, Washington may need to push for military action against the PKK leadership in northern Iraq.

Washington's ongoing support for Kurdish forces in Syria is fraught with risks for the U.S.-Turkish relationship. Since 2015, the United States has been cooperating with the Democratic Union Party (PYD) and its military wing, the People's Defense Units (YPG), to combat the Islamic State, including through the provision of weapons and technical assistance to the Syrian Democratic Forces (SDF), the Kurdish/Arab umbrella organization dominated by the YPG. Yet the PYD-YPG is an offshoot of the Kurdistan Workers Party (PKK), a Turkish group that the State Department has designated as a Foreign Terrorist Organization and which Ankara has been fighting for decades.

As will be explained below, the collective leadership of the PKK and the PYD-YPG is dominated by Turkish Kurds based in the Qandil Mountains of northern Iraq. Since 2015, when peace talks between the PKK and Ankara broke down, the group has resumed its bloody war against Turkish security forces, which has included killing civilians. If the PKK acquires U.S. arms from the YPG and uses them against Turkey, it would no doubt rupture Washington's ties with Ankara, America's oldest Muslim-majority ally and the only NATO member in the Middle East.

To mitigate the threat of such a rift, the United States should consider taking steps to significantly degrade the PKK's Turkish Kurdish leadership in Qandil. This would allow Syrian Kurds to take control of the PYD-YPG and turn their attention fully away from Turkey. Washington could then untangle its Kurdish policy in Syria from its fragile relations with Turkey.

THE PKK'S SYRIAN ROOTS

When the PKK was established in 1978, the Soviets supported it as a means of undermining U.S.-aligned Turkey. The organization first formed in Lebanon's Beqa Valley, at the time occupied by Syria. Hafiz al-Assad, father of Syria's current dictator, provided safe haven to the group's members for decades, and PKK leader Abdullah Ocalan lived in Damascus in the 1980s and the 1990s.

Following the end of the Cold War, the Syrian government continued to use the PKK as a bargaining chip in its negotiations with Turkey over water rights on the Euphrates River. At the same time, with a majority of Syrian Kurds disenfranchised and stateless under the Baath regime, Damascus saw the PKK as a way to redirect Kurdish nationalist anger away from itself and toward an "outside enemy."

Recognizing the potentially destabilizing impact of a Syria-based PKK insurgency, Ankara took steps against Damascus in September 1998, threatening invasion unless the regime stopped harboring the group. In response, Assad kicked Ocalan out and signed the Adana Protocol with Turkey, officially ending Syrian support for the PKK.

Yet because the group had been permitted to openly recruit members and disseminate propaganda in Syria for nearly two decades, it was able to form a local support base that persisted well beyond the formal severing of ties. In 2002, the PKK decided to launch franchises in Syria, Iran, and Iraq, but the PYD was the only one of these offshoots that took off.

By 2012, when Syria's civil war was in full swing and the Assad regime had vacated Kurdish areas to devote more resources to other fronts, the PYD was able to fill the void quickly. The group established three self-declared cantons in northern Syria: Afrin, Kobane, and Qamishli, collectively known as Rojava. Since 2014, the YPG/SDF have captured about 20 percent of Syrian territory with formidable U.S. military assistance. The militia also has ties with Russia, which recently deployed troops to the YPG's Afrin enclave abutting Turkey.

FIGHTING THE TURKISH KURDS' BATTLE

Although the YPG's rank and file is mostly composed of Syrian Kurds, the group is run by the PKK's largely Turkish Kurdish leadership in northern Iraq. As a May 2017 report by the International Crisis Group explained, "PKK-trained cadres" direct most of the YPG's core activities: "They decide the administration budget, appointment of front-line and regional commanders, distribution of military supplies and coordination with the U.S. military. Technocrats, mostly Ocalan sympathisers without PKK militant background, nominally run the self-rule area's formal institutions."

Furthermore, the YPG leadership structure prevents individuals without PKK credentials from gaining top positions: "Squadron and platoon commanders, who mostly joined the YPG after its 2012 creation...have little chance to advance, as the ideological academies that offer promotion prospects require long-term commitment to the PKK's struggle, directly under PKK control in Qandil." As a result, the Qandil-based PKK command -- led by Murat Karayilan, Cemil Bayik, Duran Kalkan, and Riza Altun, all Turkish Kurds -- maintains deep influence over the YPG.

Put simply, Syrian Kurds in the wider PKK family are forced to play second fiddle to Turkish Kurds, who are focused on the fight against Ankara and regard Syria as a secondary theater of operations, to be used as a lever against Turkey. This position will inevitably lead to a crisis in U.S.-Turkish ties, particularly if the PKK decides to allow the YPG's U.S.-supplied weapons to flow to its cadres in Turkey. Although the YPG leadership has promised Washington that this will not happen, PKK leaders may well push for it because a U.S.-Turkey rupture is ultimately in their interests. The question, then, is not if the YPG's American weapons will end up in the PKK's hands, but when.

FOCUSING THE PYD ON SYRIA

Fortunately, the United States can prevent such an eventuality while continuing to work with the Syrian Kurds. Washington's official policy is that the PYD-YPG is a Syrian organization, but it needs to make this axiom a reality if it hopes to avoid a rift with Turkey. That would mean convincing Turkey to launch military operations with three key objectives: hitting the PKK's underground bunker complexes in Iraq's Qandil Mountains, pressuring the group's forces in the area, and perhaps even capturing some of its senior Turkish Kurdish commanders. Any such campaign would require Washington to secure Baghdad's consent for operations in its territory, as well as to provide Turkish forces with intelligence assistance and the special munitions necessary for targeting hardened bunkers.

This policy would in turn empower the Syrian Kurds in Rojava, opening the path for them to assume full leadership over the PYD-YPG. Presumably, the group would then be fully focused on fighting the Syrian Kurdish battle for Rojava, and not the PKK's war against Turkey in Syria and beyond. Washington would also need to reassure the Syrian Kurds that it will guard their interests if they make this pivot. Meanwhile, taking concrete steps against the PKK could greatly improve U.S.-Turkish ties, which have suffered significantly in recent years.

The Syrian Kurds likely realize that they will need Washington's support well beyond the short-term fight against the Islamic State. Without U.S. backing, Rojava will fall under complete Russian control and turn into the Middle Eastern version of Transnistria, a breakaway part of Moldova that is dominated by Moscow and lacks any sort of international legitimacy. Alternatively, with Washington in its diplomatic corner, Rojava could counter the pressure emanating from Russia and the Assad regime, giving itself room to breathe and perhaps a route toward eventual autonomy inside Syria. But none of this will be possible so long as the PKK's Qandil leadership dominates the Syrian Kurdish movement, to its detriment.

Soner Cagaptay, the Beyer Family Fellow and director of the Turkish Research Program at The Washington Institute, is the author of The New Sultan: Erdogan and the Crisis of Modern Turkey.