Preparations for the events in northeastern Syria began around a year ago. Now, after the US dumped the Kurds, they have no choice but to abide by the Russian-Turkish memorandum. The Memorandum of Understanding between Turkey and Russia on northern Syria, adopted in Sochi on October 22, put an end to the Turkish offensive against the Syrian Kurds, brought northeast Syria back under the control of Damascus and guaranteed protection of Turkey’s national security interests. The Turkish-Syrian border is currently split into four stretches specified below in geographical order from east to west.
Source: Planning in the long-term: How Russia’s military operation in Syria laid groundwork for Erdogan-Putin agreement