The largely autonomous rule of Kurdish groups in north-eastern Syria could have been dealt a fatal blow after US President Donald Trump indicated the US would allow Turkey to launch an offensive.
While the Syrian Kurds are now in crisis mode, their one practical avenue to escape major losses would also probably bring renewed subjugation.
Ankara said on Tuesday that its troops could soon cross into Syria east of the Euphrates River, as US forces supporting the Syrian Democratic Forces militia alliance have begun to pull back.
Turkey says its goal is to carve a “safe zone” along the border to help neutralise the threat from the Kurdistan Workers Party (PKK), a militia group banned in Turkey.
PKK commanders and fighters make up large part of the People’s Protection Units (YPG).
The YPG comprises most of the fighters in the US-backed SDF, which includes local Arab tribal fighters and was formed by the US to fight ISIS.
The safe zone, Turkey says, would also allow Ankara to resettle Syrian refugees living in the country, although not in their original homes and towns.
Most of the nearly 4 million refugees in Turkey have fled from other regions in Syria.
Early in the civil war, Kurdish paramilitary forces began to consolidate areas in Syria's north-east that they took over as central authority weakened, or captured from Arab rebels who were fighting the Assad regime.
The YPG were in retreat in 2014 when ISIS took control of large parts of Syria's east.
But international air strikes and US support helped to push ISIS back, and eventually defeat the group, with the YPG serving as the main fighters in the campaign.
Prominent Syrian dissident Wael Sawah, who lives in exile in the US, says Washington has treated the YPG as a “single-use tool” --a disposable ally in the “war on terror”.
Now, the YPG controls vast areas in north-eastern Syria and hoped for some form of independent or autonomous region under its rule after the civil war.
The US move and the threat of a Turkish invasion has outraged Kurdish militia commanders in Syria and threatens this plan.
They have suggested they could start dialogue with the Syrian regime, Moscow or elsewhere to push Turkey back.
While Mr Trump warned Turkey on Monday that breaching his limits in its military operation would lead him to “obliterate” the Turkish economy, this appeared more aimed at Congressional Republicans furious at his move than at Ankara.
Apart from a possible intervention by Russia to mediate on behalf of the Kurds, there seems to be little to stop Turkey from invading, barring a mass international backlash and Mr Trump reversing his position.
Intervention by Moscow would erode the US position but the issue of Ankara refusing to accept the current situation indefinitely remains.
Unlike other opponents of Assad family rule in Syria, the Kurdish militias never broke ties with the regime after 2011, even as they proceeded with their own version of state building.
This dual relationship is an extension of a decades-long alliance.
The Syrian regime armed and financed the PKK between the late 1970s and the late 1990s, although the regime oppressed and disenfranchised ordinary Kurds at the same time. Thousands of educated Kurdish were tortured and imprisoned.
In the early days of the uprisings, the PKK’s surrogates in Syria resumed their co-operation with the regime, helping President Bashar Al Assad to try to put down the initially peaceful protests against his rule.
The YPG used nominal governance and violence to pacify the Arab population of the north-east. The group also crushed Kurdish dissidents and activists in the mixed, tribal region.
In past attempts to head off Turkish incursions into Kurdish held areas, YPG forces handed desert areas to the Russian and Iranian-backed regime to create a buffer zone.
The instinct of their commanders, and the Kurdish politicians they control, will be survival. Their only pathway to limit a Turkish assault may well be with the Syrian regime.
Such a deal will cost them the pursuit of Kurdish national aspirations as the YPG defines them.
The YPG is not negotiating from the position of strength it had intended when it captured so much land.