The Kurdistan Workers’ Party, known by the Kurdish acronym PKK, was founded as a Marxist-Leninist group in Turkey in 1978 in response to state-backed discrimination against Turkish Kurds, with the goal of creating an independent Kurdistan. A PKK insurgency against the Turkish state began in 1984, and fighting between the two sides has continued intermittently ever since, accompanied by heavy-handed Turkish repression in Kurdish areas, resulting in the deaths of more than 40,000 people, a majority of them Kurdish civilians. The PKK, for its part, has focused its attacks on the Turkish military over the years, but it has also hit civilian targets. Turkey and the United States have both designated the PKK a terrorist organization.
And, according to this, the Kurds first emerged in the 10th century. A majority of Kurds belong to the Shafi‘i school of Sunni Islam, but significant numbers practise Shia Islam and Alevism, while some are adherents of Yarsanism, Yazidism, Zoroastrianism and Christianity.
This then goes on to identify the SDF and it’s efforts to fight ISIS and avoiding being linked with the PKK. Turkey claims it is.
Worth reading to help understand what’s going on in the region and why Syria is rushing to the aid of the Kurds in its territory.
Article @ Why is Turkey Fighting Syria's Kurds?