[O]n Tuesday, President Vladimir V. Putin of Russia played host to President Recep Tayyip Erdogan of Turkey, for more than six hours of talks on how they and other regional players will divide control of Syria, a land devastated by eight years of civil war.



The negotiations ended with a victory for Mr. Putin: Russian and Turkish troops will take joint control over a vast swath of formerly Kurdish-held territory in northern Syria, in a move that cements the rapid expansion of Russian influence in Syria at the expense of the United States and its Kurdish former allies.

Under the terms of the agreement, Syrian Kurdish forces must now retreat more than 20 miles from the border, abandoning land that they had controlled uncontested until earlier this month — when their protectors, the American military, suddenly began to withdraw from the region.