Over the last six years, the PKK/PYD terror group has seized a quarter of Syrian territory, largely helped by the U.S.
Fourteen years after it was founded, the group, which is tied to the PKK, a group outlawed as a terrorist organization by Turkey, the U.S. and EU, has established itself along the border with Turkey.
Following the defeat of Daesh in Raqqah, the U.S. government will need new reasons to back the group, which was repackaged as the "Syrian Democratic Forces" (SDF) in October 2015.
Along with some Arab militias, the PKK/PYD has operated under the umbrella of the SDF as the U.S.'s "reliable partner" against Daesh in Syria.
The U.S. continues to provide it with arms and equipment despite Turkey's strong objections.
The PKK has waged a terror campaign against Turkey for more than 30 years, leading to the deaths of more than 40,000 people.
Imprisoned PKK leader Abdullah Ocalan gave instructions for the creation of the PKK/PYD on Feb. 10, 2002 and it forms part of the transnational political umbrella known as KCK.
Included alongside the PKK and PKK/PYD within the KCK are the PCDK in Iraq and the and PJAK in Iran.
Established on Oct. 17, 2003, the PKK/PYD took up the reins of the terrorist PKK's 20 years in Syria under Ocalan's leadership.
- Qandil
It is run on orders from PKK commanders in Qandil mountains, part of Kurdish-run territory in northern Iraq that is used to launch attacks on Turkey.
When the Syrian conflict erupted in 2011, the PKK/PYD's armed wing, known as the YPG, was established, largely with terrorists from the PKK's Iraqi camps.
Fears of Daesh's expansion saw the U.S. start to cooperate with the PKK/PYD, with U.S. support first transpiring during the September 2014 siege of Ayn al-Arab (Kobani) by Daesh.
U.S. airstrikes allowed the PKK/PYD to retake the town within months and U.S. backing for the group rose dramatically as it expanded its territory east of the Euphrates river.
After it was rebranded the SDF -- mostly to placate Turkish concerns and legitimize military aid -- the PKK/PYD crossed to the western side of the river in December 2016.
Speaking about the launch of the SDF at a security conference in Colorado two years ago, Army Gen. Raymond Thomas said: "They formerly called themselves the YPG, who the Turks would say equated to the PKK.
"So we literally played back to them that you've got to change your brand. What do you want to call yourself besides the YPG? With about a day's notice they declared that they were the Syrian Democratic Forces."
The name change added an air of legitimacy to the PKK/PYD when it came to talks about Syria's future, Thomas said. He noted that the U.S. envoy Brett McGurk "was able to keep them in the conversation".
As it captured chunks of northern Syria, the PKK/PYD stored a large amount of arms between October 2015 and April 2017, including artillery, armored vehicles, ammunition and light arms.
- Euphrates Shield
The PKK/PYD's expansion led to Turkey's Operation Euphrates Shield in August 2016, which aimed to prevent the terror group from realizing a continuous stretch of territory to the Mediterranean.
The eight-month operation to improve security, support coalition forces, and eliminate the terror threat along the Turkish border used Free Syrian Army (FSA) fighters backed by Turkish artillery and jets.
The deployment of the Turkish army and the FSA in the Al-Bab/Aza/Jarabulus triangle prevented the PKK/PYD from linked its territories in Afrin and Munbij.
In April, the Turkish Air Force struck the PKK/PYD's base in the Karacok mountains in northwest Syria, it moved its arms supplies to other sites, including U.S. bases.
The battle to take Daesh's de facto "capital" Raqqah began in June and, backed by U.S. air power, took control of the city on Oct. 17. Ten days later they began advancing on Deir ez-Zour, reaching the Iraqi border.
With less and less territory in which to confront Daesh, the U.S. administration must now seek different justification to back the PKK/PYD.
Turkey has consistently warned Washington to cut ties with the PKK/PYD.
In a telephone call to President Recep Tayyip Erdogan on Nov. 25, U.S. President Donald Trump promised to halt arms supplies to the PKK/PYD. However, his pledge was contradicted by the Pentagon, which said the U.S. was merely "reviewing pending adjustments" to military support.
Spokesman Eric Pahon said the U.S. would "continue our partnership with the Syrian Democratic Forces".
On Dec. 1, U.S. Secretary of Defense James Mattis said the U.S. would change the formation of its military in Syria.
- Talal Silo
"The YPG is armed and as the coalition stops offensive [operations] then obviously you don't need that, you need security, you need police forces, that is local forces, that is people who make certain that ISIS [Daesh] doesn't come back," he said.
Asked if that included cutting weapons to the PKK/PYD, he added: "Yeah, we are going to go exactly along the lines of what the president announced."
A former SDF spokesman who defected to the FSA, Talal Silo, last week outlined the relationship between Qandil commanders, the SDF and the U.S.
Silo said all decisions relating to the PKK/PYD in Syria were taken by Qandil. Instructions came from Sabri Ok, a senior PKK leader, Silo said.
He identified Nurettin Sofi as the head of military operations in Syria, with particular responsibility for the YPJ, the PKK/PYD's female military wing.
Silo said the SDF did not have its own fighters or independent administration but could field 50,000 fighters, 70 percent of which came from the PKK/PYD.
PKK executive council member Ferhat Abdi Sahin, who uses the codename Sahin Cilo, is on the Turkish Interior Ministry's list of most wanted terrorists, with a bounty of 4 million liras ($1.04 million). According to Silo, Cilo takes his orders directly from Ok in northern Iraq.
Cilo has supervised PKK/PYD military operations and is close to U.S. commanders.
Another figure identified by Silo was YPG commander Sipan Hamo, who controls PKK/PYD weapons dumps in Syria.
