The main Syrian Kurdish militias are known as the People's Protection Units and the (all-female) Women's Protection Units. These are two militias of the Democratic Union Party, dominant in northeastern Syria. The YPG's existence was announced in 2011 (it was apparently clandestinely formed in 2004), while the YPJ was created in the following year. Both are adherents of imprisoned Kurdish Workers' Party (PKK) leader Abdullah Öcalan's ideology of Democratic Confederalism, an anarchist-inspired political system rooted in local autonomy and feminism. The YPG/YPJ are led by General Commanders Sipan Hemo and Nessrin Abdallah respectively, and while its membership is largely Kurdish and (secular) Muslim, it includes other ethnic and religions minorities found in northeastern Syria. The groups have worked alongside local FSA units in the fight against the Islamic State, as well as Jabhat al-Nusra, but relations with the majority of the opposition are more hostile due to suspicions of both the YPG/YPJ working with the regime and fears of Kurdish calls for sovereignty.
This Arab militia is made up of members of the Shammar tribe and operates within the Hasakah governorate. The militia was formed in 2013, and was one of the original signers of the Syrian Democratic Forces founding document. The al-Sanadid Forces are led by Bandar al-Humaydi, son of tribal leader Hamidi Daham al-Hadi, and are an estimated 9,500 strong.
Jaysh al-Thuwwar is a majority Arab rebel coalition that was formed in May 2015. Jaysh al-Thuwwar is largely made up of groups formerly associated with the Syrian Revolutionaries Front and the Hazm Movement, two factions of moderate/democratic rebels who were attacked and routed by Jabhat al-Nusra and its allies months earlier in Idlib. In early 2016, it came into conflict with members of the Islamic Front and their allies in Azaz (North Aleppo), sparking an SDF offensive which resulted in the conquering of Menagh airbase and Tel Rifaat. Jaysh al-Thuwwar fields an estimated 5,000-7,000 fighters, and is active across northern Syria.
Syriac Military Council
The MFS (Matwtbo Fulhoyo Suryoyo) is a militia made up of Syriac (also known as Assyrian) Christians, associated with the Syriac Union Party. The MFS is led by Swiss-born Syriac Gewargis Hanna, who was helped found the group on 8 January 2013 in order to protect the Syriac community from Jabhat al-Nusra and Islamic State militants. The MFS is active in both the Hasakah and Raqqa governorates, as well as in Iraq's Nineveh province across the border, and fields an estimated 2,000 fighters.
Liwa Thuwar al-Raqqa
This small Arab opposition brigade active in Raqqa and Aleppo governorates. Formed in September 2012, it has spend most of its existence fighting the Islamic State, actually allying itself to Jabhat al-Nusra briefly in late 2013. In 2014, Liwa Thuwar al-Raqqa joined the Euphrates Volcano operations room, fighting the Islamic State with fellow FSA units and the YPG/YPJ. In late 2015, at the time of its joining the SDF, leader Abu Issa al-Raqqawi put the strength of Liwa Thuwar al-Raqqa at 800 men.