Who is in control in north-eastern Syria?

The region makes up more than a quarter of the entire country and is the largest area outside of the control of the Syrian president, Bashar al-Assad, and his allies. Until Turkey launched its latest offensive there on 9 October, it was controlled by the Syrian Democratic Forces (SDF), which comprises militia groups representing a range of ethnicities, though its backbone is Kurdish. The Kurds are an ethnic group of about 30 million people spread across the Middle East who have been fighting for their own state for more than a century.

Since the Turkish incursion, the SDF has lost much of its territory and appears to be losing its grip on key cities such as Tel Abyad and Ras al-Ayn. On 13 October, Kurdish leaders agreed to allow Syrian army forces to enter the cities of Manbij and Kobane to protect them from being captured by Turkey and its allies. The deal effectively hands over control of huge swathes of the region to Damascus.

That leaves north-eastern Syria divided between Syrian regime forces, Syrian opposition militia and their Turkish allies, and areas still held by the SDF – for now.

How did the SDF come to control the region?

Before the SDF was formed in 2015, the Kurds had created their own militias who mobilised during the Syrian civil war to defend Kurdish cities and villages and carve out what they hoped would eventually at least become a semi-autonomous province within Syria.

In late 2014, the Kurds were struggling to fend off an Islamic State siege of Kobani, a major city under their control.

Enter the US. The Americans had been desperately searching for a reliable partner to help them fight Isis. They had spent $500m training and equipping other Syrian rebel groups without success. In the Kurds – effective fighters, whose political leaders were secular and advocated modern values such as gender equality – they saw a group with whom they could ally.

With US support, including arms and airstrikes, the Kurds managed to beat back Isis and went on to win a string of victories against the radical militant group. Along the way the fighters absorbed non-Kurdish groups, changed their name to the SDF and grew to include 60,000 soldiers.

“Without [the SDF], President Donald Trump could not have declared the complete defeat of Isis,” said Gen Joseph Votel, the American commander of operations in Syria who struck the alliance with the Kurds in 2015. The SDF suffered 11,000 casualties in the battle against Isis.

Facebook Twitter Pinterest An SDF commander waves the group’s flag in Raqqa, formerly an Isis stronghold. Photograph: Bülent Kılıç/AFP/Getty Images

Why does Turkey oppose the Kurds?

For years, Turkey has watched the growing ties between the US and SDF with alarm. Significant numbers of the Kurds in the SDF were also members of the People’s Protection Units (YPG), an offshoot of the Kurdistan Workers’ party (PKK) that has fought an insurgency against the Turkish state for more than 35 years in which as many as 40,000 people have died. The PKK initially called for independence and now demands greater autonomy for Kurds inside Turkey.

Turkey claims the PKK has continued to wage war on the Turkish state, even as it has assisted in the fight against Isis.

The PKK is listed as a terrorist group by Turkey, the US, the UK, Nato and others and this has proved awkward for the US and its allies, who have chosen to downplay the SDF’s links to the PKK, preferring to focus on their shared objective of defeating Isis.

What are Turkey’s objectives on its southern border?

Turkey aims firstly to push the SDF away from its border, creating a 20-mile (32km) buffer zone that would have been jointly patrolled by Turkish and US troops until Trump’s recent announcement that American soldiers would withdraw from the region.

Officials in Ankara signalled on 13 October that they may seek to go further than the buffer zone in this current military operation.

The Turkish president, , has said he would seek to relocate more than 1 million Syrian refugees in this “safe zone”, both removing them from his country (where their presence has started to create a backlash) and complicating the demographic mix in what he fears could become an autonomous Kurdish state on his border.

How would a Turkish incursion impact on Isis and stability of the wider Middle East?

Nearly 11,000 Isis fighters, including almost 2,000 foreigners, and tens of thousands of their wives and children, are being held in detention camps and hastily fortified prisons across north-eastern Syria.

The SDF has been pleading for international assistance in dealing with these prisoners, who countries including the US, UK and Australia have been reluctant to take back – in some cases cancelling the citizenship of prisoners.

Facebook Twitter Pinterest A guard at the al-Hawl refugee camp in northern Syria. Photograph: Achilleas Zavallis/The Guardian

SDF leaders have warned they cannot guarantee the security of these prisoners if they are forced to redeploy their forces to the frontlines of a war against Turkey. They also fear Isis could use the chaos of war to mount attacks to free their fighters or reclaim territory.

On 11 October, it was reported that at least five detained Isis fighters had escaped a prison in the region. Two days later, 750 foreign women affiliated to Isis and their children managed to break out of a secure annex in the Ain Issa camp for displaced people, according to SDF officials.

Two Isis prisoners, part of team of British prison guards nicknamed the “Beatles”, who tortured and murdered hostages including the American photojournalist James Foley, were handed over to US officials in the hours before the Turkish incursion commenced on 9 October.

It is unclear which detention sites the SDF still controls and the status of the prisoners inside.

After four days of relentless bombardment from the Turkish side, the SDF on 13 October struck a deal to allow Syrian army forces to enter their territory from the west. The agreement puts Syrian soldiers on a collision course with Turkish troops and their Syrian militia allies. It is not clear if their fighters will actually clash – they have been reluctant to do so in the past – nor how much formerly Kurdish-held land the Turkish side and Syrian government respectively will seek to claim. But with two armies on the move (one of them, Turkey, a Nato ally), and pockets of US troops still in the conflict zone, the potential for escalation is high.