Origins of the Syrian Democratic Forces: A Primer | Syria Deeply, Covering the Crisis
▻http://www.syriadeeply.org/articles/2016/01/9346/origins-syrian-democratic-forces-primer
The Syrian Democratic Forces, or SDF, is a coalition of Kurdish, Sunni Arab and Syriac Christian fighters, but is completely dominated by its Kurdish element, which is a powerful and well organized militia known as the Popular Defense Units, YPG, with an all-female branch called the Women’s Defense Units, or YPJ. These organizations, in turn, are Syrian front groups for the Kurdistan Workers’ Party or PKK. The other militias involved in the Syrian Democratic Forces are either long-standing PKK allies or proxies, such as the armed wing of the Syriac Union Party, or more recent allies drawn from the Sunni Arab tribal landscape in this part of Syria and from the remains of small Sunni Arab rebel groups crushed by the so-called Islamic State.
The coalition as a whole receives American air support for operations against Islamic State, as did the YPG/J before it. That started in the Battle of Kobane that began in autumn 2014, which was enormously successful—really the first major battlefield defeat inflicted on Islamic State. It has provided the template for US-PKK cooperation. In addition, the Pentagon has picked out a number of these little Arab groups that work under the SDF umbrella as favored recipients of arms and support. It terms them, collectively, the Syrian Arab Coalition, though no one else seems to use that name.