Kurdish militia and US forces control a large part of Syria consisting of almost all the land east of The Euphrates, and some part west of the river. It has for a long time been the goal of USA to break up Syria in several smaller states.
According to Syrian Girl the war in Syria end if US forces left the country; Kurdish militia would ally with Syrian forces to defend against a Turkish invasion. Remaining terrorist groups would be defeated and Turkish forces would leave the country. The areas held by US backed Kurdish militia have 80 % of Syrian oil and a large part of the counties wheat crops which Kurdish militia now have started to burn down. See the interview below for more details.
Map over the military situation in Syria, 2019-06-26 (area held by US backed Kurdish militia marked in orange):