On a muddy trail in northern Syria, the war’s newest exiles are leaving. Most are Kurds, fleeing Afrin for the regime-held city of Aleppo, just over a grey horizon. Behind them, Turkish troops and Arab forces they sponsor have encircled their home city except for the squeeze point they used to flee. Ahead, Shia militants allied to the Syrian army man checkpoints deciding who can pass.

With Syria’s war ticking over into its eighth gruelling year, the north of the country is once more on the move. The Kurds are bearing the brunt of the latest upheaval, fleeing their enclave near the Turkish border as a promised storming of Afrin draws near. At least 250 civilians have been killed in the bombardment of Afrin as the Turks and their proxies have advanced. Many abandoning the majority-Kurdish enclave fear they may not be allowed to return when – and if – the dust finally settles on this war without restraint. On Sunday morning, the Turkish backed Free Syrian Army rebels said they had entered the town after Kurdish forces pulled out. Everything appears up for grabs now: their homes, futures and even the Kurdish cause.

“We sat this out for the past seven years,” said Hero, a Kurdish resident of Afrin who had made it to Aleppo. “We bothered no one and watched the storm pass all around us. Then the Turks came for us.”

A safe haven in the tempest of Syria, Afrin had avoided the war in the rest of the north until a Turkish-led incursion into its surrounding hills seven weeks ago. Idlib and Aleppo, not far away, had been ravaged by jets and insurgency. Afrin, meanwhile, had been a haven for refugees from elsewhere. Arabs, Kurds, Turkmen, Christians, Muslims, even Yazidis from Iraq, had hunkered down as war raged all around.

Even as Afrin’s civilian leaders showcased the city as a model of coexistence amid the chaos, it became a microcosm of the potent geopolitics that subsumed local allegiances. Arab-Kurdish tensions simmered in the north. But more importantly a once workable relationship between Washington and Ankara broke down – with the postwar future of Syria’s Kurds central to the schism.

Afrin’s transformation into a focal point of the Syrian conflict began on 20 January, shortly after the Pentagon announced it would raise a border militia from a Kurdish-led force it had formed in north-eastern Syria to fight the Islamic State (Isis) terror group. Washington’s alliance with the Kurds had never sat well with Ankara, which regarded their leaders as being ideological allies of the militant Kurdistan Workers’ party (PKK), whose insurgency in south-eastern Turkey it continues to fight.

Faced with American assurances that the alliance would be temporary, Turkey had stood by as Isis was swept from the towns and cities of north-eastern Syria, culminating in the extremists’ ousting from Raqqa late last year.

But the mooted border force was a step too far for wary officials, a sign that the Kurds – aided by their backers – would make strategic gains which could weaken Turkey’s hold on its 500-mile frontier with Syria. And so, on 20 January, Turkey’s leaders, angered by Washington but not willing to confront the Kurds where they fought alongside the Americans, instead turned their guns on Afrin, a small pocket of north-western Syria, far from the fight with Isis and with no presence of US troops.

A gap of around 60 miles separates Afrin from the US-backed Syrian Democratic Forces’ presence to the east, roughly demarcated by the Euphrates river. Turkey has carved out a sphere of influence between the Kurdish populations, building its stocks with local Arab communities, intervening in the Syrian war when it wants to – but most importantly, keeping the Kurds apart.

“They say that the fighting groups in Afrin and Rojava (north-eastern Syria) are the same, and that is basically true,” said a western diplomat based in the region. “Equally true is that the militants in Afrin had not pointed a gun their way until the Turks sent their air force after them.”

The Kurds fleeing Afrin and those who have stayed behind – up to 200,000 people are thought to remain in the city – say they fear that Turkey aims to change the demography of the town, and by extension the border. The Arab force it is using comprises members of the Free Syria Army and allied militias and was raised to fight the Assad regime. Now, though, the spectre of Arabs being sent to fight Kurds in a majority-Kurdish city adds a troubling dimension to a conflict that continues to lurch far from the original battlelines of a nationalistic push to oust the Syrian leadership.

Inside Afrin, a group of Arab students praised the Turkish incursion last week, insisting that civilians were not indiscriminately targeted as they repeatedly have been in Ghouta, near Damascus, over the past month of airstrikes by Syrian and Russian jets. “They have not been perfect,” said Dawood Mahmoud, who fled to Afrin from a nearby town more than a year ago. “But their mistakes are just that – mistakes.”

A Kurdish resident of the city, who has not been given permission to leave by Kurdish militant groups, said the opposite. “Last night they bombed the hospital, and last week they blew up the waterworks. There have been up to 500 civilians killed. This is barbaric.

“They have been dropping leaflets telling us to trust them and surrender. They think we’re fools. Neither they nor their Arabs can take Afrin. They wouldn’t dare. This will be a blockade like Aleppo.”

As the siege closes in, and as Syrians of all sects and ethnicities crisscross the battered north, the war is drifting further from resolution than ever before. The plaintive cries of the global aid community remain mostly ignored, as do the demands of United Nations leaders. “Basically, anything goes,” said the western official. “There is no right or wrong any more. The international order is dying in the ruins of Syria.”