Since the Kurdish authorities have asked President Bashar al-Assad's government for help, thousands of Syrian army forces have flooded into northern Syria for the first time since the government lost control of the region several years ago.
But Syrian government troops remained far from the border region near Ras al-Ain, where Kurdish troops were fighting alone. Instead, government forces are positioned in other strategic positions, such as the western cities of Manbij, to help ease pressure on Kurdish frontline fighters.
The last-minute union comes with a hefty price tag for the Kurdish authorities, who are virtually giving up self-government.
Syrian Kurdish militias set up a system of self-government in northern Syria in 201
The fighters expanded their territory significantly after partnering with an international military coalition led by the United States to push the Islamic State out of the area.
After the Kurdish-led troops conquered ISIS, they assumed responsibility for its management, ultimately controlling roughly a quarter of the Syrian land. They also guard thousands of ISIS fighters and their families, hundreds of whom escape from a detention camp in Ras al-Ain after Turkish-led forces bombard the area.
Control of Kurds over land in Syria has angered Turkey, as militia is the offspring of a guerrilla group that has waged decades-long rebellion against the Turkish state. Turkey has long been pushing the United States to abandon its alliance with Kurdish fighters so that Turkish troops can enter Syria and force Kurds out of territory near the border.
Washington has rejected Turkey's demands for several years, maintaining a de facto peacekeeping presence. border near Ras al-Ain, the city in the center of Friday's fighting. But that changed last week when Mr Trump made a sudden decision to withdraw troops, first from that particular area and later from all over northern Syria.
Carlotta Gall reported from Ceylanpinar and Patrick Kingsley from Istanbul.