BBC- The United States is unexpectedly pulling its troops from the border between north-eastern Syria and Turkey, raising questions over the fate of the area.
It will allow the Turkish military to launch an operation there against a Kurdish-led militia alliance that Western powers relied on to defeat the Islamic State (IS) group.
We’ve boiled down why it matters.
Why is Turkey planning an assault?
One main reason: Turkey considers the biggest militia in the Kurdish-led alliance a terrorist group. It says it is an extension of a Kurdish rebel group fighting in Turkey.
Turkish leaders want a 32km (20-mile) deep “safe zone” along the Syrian side of the border clear of Kurdish fighters. They also hope to resettle up to 2 million Syrian refugees currently living in Turkey there.
The Kurdish-led alliance says it will defend its territory and that the US is “leaving the area to turn into a war zone” and risking the re-emergence of IS.
Turkey has vowed to push back from its border members of a Syrian Kurdish militia called the People’s Protection Units (YPG).
Turkish leaders view the YPG as an extension of the banned Kurdistan Workers’ Party (PKK), which has fought for Kurdish autonomy in Turkey for three decades.
The YPG dominates an alliance of Kurdish and Arab militias called the Syrian Democratic Forces (SDF), which has driven IS out of north-eastern Syria over the past four years with the help of air strikes by a US-led multinational coalition.
Despite the threat posed by IS, Turkey condemned the US for supporting the YPG.
In 2018, Turkey attacked the Kurdish-controlled of Afrin, in western Syria. Dozens of civilians were killed and tens of thousands displaced.
That December, with IS close to defeat, President Donald Trump said the US would begin withdrawing its troops from Syria. When commanders and allies expressed concern about the fate of the Kurds, he vowed to “devastate Turkey economically” it attacked them and proposed a “20-mile safe zone” along the border.
Mr Trump later suspended the withdrawal, but Turkish President Recep Erdogan continued pressing for a safe zone.
In August, the US and Turkey agreed to establish one together. Kurdish officials expressed support and the YPG dismantled border fortifications.
But two months later, the White House said Mr Trump had decided to let Turkish troops cross into Syria to set up a safe zone alone.
Turkey will take responsibility for captured IS militants there. The SDF is holding 12,000 men suspected of being IS members, and 70,000 women and children, many of them related to IS fighters.
The SDF says it has been “stabbed in the back” by the US and will defend north-eastern Syria “at all costs”. A Turkish offensive will create a “permanent warzone” and reverse the defeat of IS, it warns.