When ISIL invaded the Sinjar Mountains in 2014 and began to massacre its Yezidi population, the PKK intervened with hundreds of fighters in order to save the locals from the Islamic State militants.
Since then, the PKK set up two local Yezidi self-defense groups, namely the Sinjar Resistance Units and the Êzîdxan Women's Units.
In late 2015, anti-ISIL forces finally succeeded in driving the Islamic State mostly from the Sinjar area, but the PKK fighters have since refused to leave and continue to train and equip the local PKK-affiliated militias.
This has caused resentment among the Kurdistan Democratic Party (KDP), which regards Sinjar as part of Iraqi Kurdistan and sees the PKK as local political rival.

The KDP believes that the presence of the PKK in Sinjar is illegal, and that their own Peshmerga forces are the only legitimate security force of the area.
The Rojava Peshmerga are Syrian Kurdish fighters affiliated with the KNC, which in turn was set up by the KDP, and effectively operate as part of the KDP's regular armed forces.
When ISIL invaded the Sinjar Mountains in 2014 and began to massacre its Yezidi population, the PKK intervened with hundreds of fighters in order to save the locals from the Islamic State militants. Since then, the PKK set up two local Yezidi self-defense groups, namely the Sinjar Resistance Units and the Êzîdxan Women's Units. In late 2015, anti-ISIL forces finally succeeded in driving the Islamic State mostly from the Sinjar area, but the PKK fighters have since refused to leave and continue to train and equip the local PKK-affiliated militias. This has caused resentment among the Kurdistan Democratic Party (KDP), which regards Sinjar as part of Iraqi Kurdistan and sees the PKK as local political rival.
The KDP believes that the presence of the PKK in Sinjar is illegal, and that their own Peshmerga forces are the only legitimate security force of the area. The Rojava Peshmerga are Syrian Kurdish fighters affiliated with the KNC, which in turn was set up by the KDP, and effectively operate as part of the KDP's regular armed forces.
Sinjar clashes (2017)