The withdrawal followed a late Sunday statement by the White House that the United States would not intervene in a long-threatened Turkish offensive into northern Syria. The announcement, which signaled an abrupt end to a months-long American effort to broker peace between two important allies, came after a call between President Trump and Turkish President Recep Tayyip Erdogan…

The fast-moving developments threatened a fresh military conflagration in a large swath of northern Syria, stretching from east of the Euphrates River to the border with Iraq. Syrian Kurds had established an autonomous zone in the area during more than eight years of Syria’s civil war.

Ankara, however, has been increasingly unnerved by the Kurdish presence, and by the close ties between U.S.-allied Syrian Kurdish fighters and the Kurdistan Workers’ Party, or PKK, a militant group that has fought a long insurgency against the Turkish state.