There were some 2000 US troops in eastern Syria too, but it was the Kurds who bore the brunt of the fighting and the casualties. Indeed, a principal role of the US forces was to deter Turkey from attacking the Kurds, because Turkey, at war with its own big Kurdish minority, strongly opposed the Syrian Kurds' ambition for independence.
But now Islamic State has been destroyed (or, at least, so Donald Trump believes) and the US has no further need of the Kurds. Time to throw them away.
Deprived of US air support, the Syrian Kurds have little hope of resisting a Turkish invasion.
As Turkish Defence Minister Hulusi Akar said on Thursday: "They can dig tunnels or ditches if they want ... . When the time and place come, they will be buried in their ditches."
So where can the Kurds turn?
Only to Damascus, where Syrian dictator Bashar al-Assad has sworn to recover "every inch" of Syrian territory from the various rebel militia forces that controlled different parts of the country.
All that remains to fulfil that ambition is the recovery of Idlib province in the northwest — still held by Turkish-backed Islamist extremists — and of the Kurdish-controlled northeast of the country.
For the Syrian Kurds, reeling from the American betrayal, the urgent, unavoidable question has become: Would you rather be conquered by the Turks or by Assad? There is no third option: the dream of independence is dead.
When Turkey conquered the much smaller Kurdish-majority enclave of Afrin in northwestern Syria last February, almost every Kurd in the territory was driven into exile.
Assad's rule is unattractive, but the Syrian Kurds have carefully avoided fighting his forces (they only fought IS), and they might be able to cut a deal that left them some local autonomy. After all, Assad doesn't want the Turks taking control of eastern Syria either.
The Kurds aren't fools and, as the likelihood of an American defection grew in the course of this year, they sent several delegations to Damascus to see what Assad would offer.
They came back disappointed, because Assad did not want to do anything that would open the door to a federal state in Syria, and he quite rightly thought that he had the upper hand. But now that the US pull-out from eastern Syria and the Turkish invasion of the same region have both become imminent realities, he may want to think again.
This is a part of Syria rich in oil, water and wheat. Assad needs its resources to rebuild the country, and a Turkish occupation could be a long-lasting affair. It's therefore possible that he will make a deal with the Syrian Kurds to keep the region in Syrian hands.
The return of the Syrian army would be tricky to manage, since it would have to arrive in each part of the region after the Americans left (to avoid clashes) but before the Turks arrived. Moreover, the Syrian army is seriously short of manpower, and this operation would require a lot of it.
All the more reason to give the YPG a continuing role in the region's security, the Kurds might argue, and it's not impossible that Assad might buy that argument, provided that the Kurdish militia became (at least in theory) a part of the Syrian army.
So the Russians may be right. When Trump revealed via Twitter that he was going to pull all American forces out of Syria, Russian foreign ministry spokeswoman Maria Zakharova responded that the US decision could result in "genuine, real prospects for a political settlement" in Syria. And it's true.
Turkey could be convinced (by the Russians) that letting Assad take control of Kurdish-majority parts of Syria is enough to end the alleged Kurdish "threat" to Turkish security.
Then only the single province of Idlib would remain beyond Assad's reach, and that's not really a critical issue.
In fact, the fix could be in already. We'll know shortly. But no matter what, the Kurds lose again. Of course.
■Gwynne Dyer's new book is Growing Pains: The Future of Democracy (and Work).
