In a phone call on Friday, Donald Trump told Turkish president Recep Tayyip Erdoğan that the U.S. would stop arming Kurdish fighters in Syria.

Erdoğan had been agitating against arming the Kurds in Syria for years, saying the arms were being funneled to the Kurdish Workers Party (PKK) militia.  NATO has designated the PKK as a terrorist group for its armed attacks inside Turkey.

U.S. arms were being supplied to the YPG, a Kurdish militia Turkey says has ties to the PKK.  Arming the Kurds had been a major source of tension between the two countries.

Chicago Tribune:

In late afternoon, the White House confirmed the weapons cutoff would happen, though it provided no details on timing.

"Consistent with our previous policy, President Trump also informed President Erdogan of pending adjustments to the military support provided to our partners on the ground in Syria, now that the battle of Raqqa is complete and we are progressing into a stabilization phase to ensure that ISIS cannot return," the White House statement said, referring to the recent liberation of the Syrian city that had served as the Islamic State's de facto capital.

The decision to stop arming the Kurds will remove a major source of tension between the United States and Turkey, a NATO ally. But it is likely to further anger the Kurds, who already feel betrayed since the United States told them to hand over hard-won territory to the Syrian government.

Turkey has pointed to the YPG's affiliation with the Kurdistan Workers' Party – a Kurdish rebel group that has fought the Turkish state for decades – as evidence of its terrorist ties. The YPG, which formed amid the chaos of the Syrian civil war, has worked with U.S. forces to oust the Islamic State from key areas there.

The Obama administration began arming the Syrian Democratic Forces, which is dominated by the Kurdish YPG militia, because they were considered the most effective fighters against Islamic State militants.

The phone call between Trump and Erdogan followed a summit on Syria held this week in Sochi, Russia. It was attended by Erdogan, Russian President Vladimir Putin and Iranian President Hassan Rouhani. Russia and Iran backed the government of Syrian President Bashar Assad and helped Syrian forces to rout the Islamic State.

The two powers, along with Turkey, have forged an alliance that is advancing its own peace plan, in which the United States would play little role beyond being an observer. They have said U.S. troops should leave Syria now that the Islamic State's defeat appears imminent.

But a U.S. withdrawal without a peace plan well on its way would be victory for Assad, and by extension, Iran and Russia.

The Kurds are a minor player in a strategic part of the world.  The U.S. fully understands their desire for an independent state but also knows the impossibility of that dream at the present time.  The Kurds are spread out in an arc from Syria through Iraq into Iran, Turkey, and Armenia.  The idea that all five of those states would allow a carve-out of their territory to satisfy Kurdish ambitions is absurd. 

So the Kurds are trapped by history and events.  As our most reliable and skillful ally in Syria, the Kurds performed very well.  But the present realities regarding Turkey make continued support for the Kurds problematic.

It may seem like weakness to cave in to Erdoğan's demands, but once again, reality intrudes.  Turkey is a member of NATO, despite electing an Islamist president.  Turkey has always played a vital role as a western bulwark against Russian expansion into southern Europe, and despite all, it continues to play that role today. 

Americans have had a special place in their hearts for the Kurds.  In Iraq, the Kurds are very pro-American and welcomed U.S. troops stationed there.  But our support for the Kurds can go only so far before it bumps into other foreign policy realities.  It's unclear how that will affect our relations with the Kurds, but it almost certainly won't help to improve them.