The US forces in northern Syria long served as a de facto buffer force, positioned in between Turkey and both the Syrian government and Syrian Kurds. With US forces withdrawing, Russia is taking over that role, moving into that space the US formerly filled.

For Russia, it’s a bit more pro-active than what the US was doing. Russia describes its forces as patrolling along the “line of contact” between Turkey and Syria, and that’s a key aspect of why they are there. In addition to patrols, Russia has also taken over at least one former US base in the area, one hastily abandoned by US forces.

Russia, after all, is a close ally to Syria, and keen to support them. At the same time, Russia has tried to maintain ties with Turkey to keep the situation on the border from falling apart. Even now, Russia is engaging with both parties.

That’s something the US would’ve never done as a buffer force. The US has ties with Turkey as a consequence of NATO membership, and was aligned with the Kurdish forces in Syria, but refused to officially talk with Syria, and US diplomats seemed to go out of their way to undercut any regional diplomacy on Syria, believing it would weaken their vision for a post-war Syria, a regime change and a US-friendly government replacing a long-standing Russian ally. The US never thought much of anyone else’s goals, even the Kurds’ hopes for autonomy were dismissed by US officials who wanted a strong central government in Syria.

That the US cut the Kurds loose surprised no one, least of all the Kurds. While the US had tried to keep them from publicly negotiating with the Assad government, for the past year Kurdish officials had kept secret back channels to Damascus and Moscow wide open, meaning when the Trump Administration decided that the Kurds were no longer an American interest, they had options on who to turn to.

While it’s not clear what Russia is going to do for the Syrian Kurds, their presence at all likely complicates parts of the Turkish invasion, particularly where they are coming up against Kurdish towns that were handed over to the Syrian government to defend. The last thing Turkey wants is to start a fight with Russia on foreign soil.