The YPG-PKK connection
https://www.atlanticcouncil.org/blogs/menasource/the-ypg-pkk-connection/
In mid-July 2012, the Syrian government withdrew its forces from a large amount of territory along the Turkish border. This move allowed the Democratic Union Party (PYD), a Kurdish nationalist group linked to the Kurdistan Workers’ Party (PKK)—a US- and Turkish-designated terrorist group—to take administrative and military control over the self-declared cantons of Efrin, Kobani and Jazira, collectively named Rojava. The link between the PYD and PKK challenges Turkey’s interests in Syria and, by its own estimate, its national security.
To support the PYD’s political and military efforts in Syria, Kurds from Turkey, Iran, and Iraq have travelled to Syria to join with the People’s Protection Units (YPG), the PYD’s militia. The growing sense of cross-border pan-Kurdish nationalism has contributed to the resurgence in violence in Turkey’s southeast, following the break-down of peace talks in mid-July 2015 between the Turkish government and the PKK. In an interview with the International Crisis Group, an unidentified PKK member underscored the importance of Rojava, describing the war in northern Syria as a historic opportunity to implement its program of “democratic self-administration,” a system of governance based on imprisoned PKK leader Abdullah Öcalan’s teachings.