BEIRUT (Reuters) - The future of Kurdish-led swathes of northern and eastern Syria has been thrown into doubt by President Donald Trump’s decision to withdraw U.S. troops who have helped secure the territory.

FILE PHOTO: Kurdish fighters from the People's Protection Units (YPG) head a convoy of U.S military vehicles in the town of Darbasiya next to the Turkish border, Syria April 28, 2017. REUTERS/Rodi Said/File Photo

The region, roughly a quarter of Syria, is the largest chunk of the country still outside the control of President Bashar al-Assad, who is backed by Russia and Iran.

Syrian Kurdish leaders fear Turkey, which sees them as a threat, will use a U.S. pullout as an opportunity to mount an assault into northern Syria.

This has driven them to talk to Moscow and Damascus in the hope of agreeing a deal to protect the region and safeguarding their political gains.

In tweets on Monday, Trump threatened NATO ally Turkey with economic devastation if it attacks the U.S.-allied Kurdish fighters, drawing a sharp rebuke from Ankara.

(Syria control map: tmsnrt.rs/2RgCxxb)

HOW DID THE KURDS EMERGE AS A FORCE?

The main Syrian Kurdish faction, the Democratic Union Party (PYD), began to establish a foothold in the north early in the war as government forces withdrew to put down the anti-Assad uprising elsewhere. An affiliated militia, the People’s Protection Units (YPG), secured the region.

Early in the conflict, their control was concentrated in three predominantly Kurdish regions home to roughly 2 million Kurds. Kurdish-led governing bodies were set up.

The area of YPG influence expanded as the fighters joined forces with the U.S.-led coalition against Islamic State (IS), becoming the spearhead of a multi-ethnic militia alliance, the Syrian Democratic Forces (SDF).

SDF influence widened to Manbij and Raqqa as IS was defeated in both. It has also reached deep into Deir al-Zor, where the SDF is still fighting IS. The SDF, which also includes Arab and other groups, says it has more than 70,000 fighters.

Kurdish leaders say their aim is regional autonomy within a decentralized Syria, not independence.

WHY DOES TURKEY VIEW THEM AS A THREAT?

The PYD is heavily influenced by the ideas of Kurdish leader Abdullah Ocalan, a founding member of the Kurdistan Workers’ Party (PKK), which has waged a 34-year insurgency in Turkey for Kurdish political and cultural rights. Ocalan has been in jail since 1999 in Turkey. He is convicted of treason.

The PKK is designated a terrorist organization by Turkey, the United States and the European Union. Turkey says the PKK is indistinguishable from the PYD and YPG.

Turkey has a Kurdish minority equal to 15 to 20 percent of its population, mostly living in eastern and southeastern areas bordering Syria. Wary of separatistism, Turkey views the PYD’s Syrian foothold as a security threat.

Syria’s main Kurdish groups do not hide Ocalan’s influence: they organized elections toward establishing a political system based on his ideas.

Turkey has already mounted two cross-border offensives in northern Syria as part of its efforts to counter the YPG.

FOR KURDS, IS ASSAD A FRIEND OR FOE?

Syria’s Baathist state systematically oppressed the Kurds before the war. Yet the YPG and Damascus have broadly stayed out of each other’s way during the conflict, despite occasional clashes. They also have been seen to cooperate against shared foes, notably in and around Aleppo.

The YPG has allowed the Syrian state to keep a foothold in some of its areas. The YPG commander told Reuters in 2017 it would have no problem with the Assad government if Kurdish rights are guaranteed in Syria.

But Damascus has long opposed Kurdish autonomy demands and talks between the two sides last year went nowhere.

Kurdish-led authorities presented a roadmap for a deal with Assad at recent meetings in Russia and is awaiting a response, a senior Kurdish official told Reuters this month.

A Syrian government minister showed optimism last week over dialogue with Kurdish parties and said conditions were ripe for them to return to the state.

WHAT WOULD AN ASSAD-KURD DEAL MEAN FOR THE WAR?

The territory held by Damascus and the Kurdish-led authorities accounts for most of Syria. A political settlement - if one could be reached, perhaps with Russian help - could go a long way to stitching the map back together.

But it would not mark the end of the war.

Anti-Assad insurgents, though defeated across much of Syria by the government and its allies, still have a foothold in the northwest stretching from Idlib through Afrin to Jarablus. Turkey has troops on the ground in this area.

The rebels include Turkey-backed Free Syrian Army groups and jihadists.

Enmity runs deep between the YPG and these groups.

For the YPG, one priority is recovering Afrin from the rebels who seized it in a Turkey-backed offensive last year.

Assad also wants Turkey out as he vows to recover “every inch” of Syria.