ERBIL, Iraq—Turkey and the United States might be headed for a showdown: NATO army against NATO army—the two biggest armies, in fact, in the alliance.

But this is the Middle East, where nothing is simple. And precisely because the potential for catastrophic violence is so high, conflicts often fester rather than explode. The scene of the looming confrontation, moreover, is Syria—a battleground where alliances, allegiances, tactics, and strategies shift like flow charts seen through a kaleidoscope.

The proximate cause of the looming crisis is an offensive by the Turkish army and forces it supports against the largely Kurdish-controlled city of Afrin in Syria’s Aleppo province near the Turkish border.

The offensive started over the weekend after U.S. officials revealed plans last week to stay in Syria and develop what was described as a “border force” of some 30,000 Syrian Kurdish soldiers. This was portrayed in Washington as a key development in the Trump administration’s strategy to keep the so-called Islamic State from coming back and help displaced people return to their homes. Some 2,000 American troops are on the ground in Syria in Kurdish-controlled regions to advise, assist, and help to organize the forces there.

Yet by the end of the week—facing Turkish outrage—the Trump administration was backpedaling frantically, rushing to say this wouldn’t be a “conventional” border force. Administration officials told The Wall Street Journal “the plan was poorly conceived and won’t proceed as previously outlined by the military.”

The fact of the matter is that the U.S.-backed Kurdish fighters played a central role defeating the so-called Islamic State on the ground in what was once its “caliphate”: a victory for which the Trump administration is quick to claim credit. And some of those same Kurdish fighters , known as the People’s Protection Units or YPG, are the ones now under Turkish assault in Afrin.

The Turks insist the YPG is a terrorist organization allied to the PKK guerrillas who have waged a decades-long war against Ankara. The YPG and the Pentagon have denied this.

“ The Pentagon plan was ‘poorly conceived and won’t proceed as previously outlined by the military.’ ”

But putting aside what’s called “creative ambiguity” in Foggy Bottom, in the war against ISIS the salient fact is this: At the height of the ISIS offensives in Iraq and Syria in 2014 and 2015 the Kurds were the only force that stood against it resolutely, relentlessly, and at great cost.

The massacre and enslavement of the Yazidi population in and around the strategic city of Sinjar in Iraq, for instance, would have been even worse had the YPG not deployed fighters to rescue many thousands of people—eventually with U.S. air support.

In the hard-fought battle of Kobani on the Syrian-Turkish border in the autumn of 2014, once again the YPG stood its ground, eventually with U.S. and other coalition air support, and finally handed ISIS a critical defeat that shattered its mystique of invincibility. Throughout that battle, Turkish troops and tanks looked on, doing absolutely nothing to impede the ISIS terrorists. At the same time, thousands of foreign fighters anxious to join the ISIS ranks had discovered they could move easily—by some accounts, freely—through Turkey into Syria.

Then, as now, Ankara’s main objective was to crush the Kurdish insurgents ; defeating ISIS was, at most, a secondary concern.

Through three long years, the Pentagon built its rapport with the YPG, training and equipping its forces, supporting them with air power, and helping them to integrate Arab fighters under the umbrella of the YPG-dominated Syrian Democratic Forces, or SDF, which took the vanguard in the savage fighting that finally liberated, at enormous cost, the ISIS “capital” of Raqqa in Syria.

“ Throughout that battle of Kobani, Turkish troops and tanks looked on, doing absolutely nothing to impede the ISIS terrorists. ”

And yet… and yet, after Turkey attacked Afrin over the weekend the U.S. response was muted, to say the least, and sounded very much like a green light for Ankara to continue the attacks it dubbed “Operation Olive Branch” in order to create what Turkey is defining as its own “security zone.”

U.S. Secretary of Defense James Mattis, speaking of the Turkish bombing raids that opened the offensive, said on Sunday that the Americans got a head’s up from Ankara.

“They warned us before they launched the aircraft that they were going to do it,” he told reporters traveling with him to Southeast Asia, even as he declined to say whether the U.S. tried to warn the Turks off. “We are very alert to it. Our top levels are engaged… and we’re working through it. We’ll work this out.”

U.S. Secretary of State Rex Tillerson was similarly subdued. “Turkey has legitimate concerns about terrorists crossing the border into Turkey and carrying out attacks, and we—we appreciate their right to defend themselves,” Tillerson told reporters on Monday en route to Paris.

“But this is a tough situation where there’s a lot of civilians mixed in, so we’ve asked them to just try to be precise, try to limit your operation, try to show some restraint, let us see if we can work with you to create the kind of security zone you might need,” he added.

As the Kurds understand it, the American message to them is that in Afrin they are on their own. And given the spheres of influence in the fractured Syrian state, that is not altogether surprising. Afrin is in what might be called the Russian zone, and several hundred Russians were based there—until, in an evident arrangement with Ankara—they pulled out.

“ What will happen if the Turks decide to move against areas where there is a substantial presence of American advisers? ”

While the Americans have troops in a large part of northern Syria, they don’t have any troops in Afrin. The Russians pulled out their units from Afrin in an apparent deal with Turkey, after the Kurds refused to hand over Afrin to the Syrian regime.

The big question now is what will happen if the Turks decide to move against areas where there is a substantial presence of American advisers and support.

The city to watch is Manbij, a town about 30 miles from the Turkish border, not far from Kobani, that had a population of some 400,000 people before the war and is an important center for the Kurds and their U.S. military partners.

“Turkey is not conducting any offensive operations in Manbij. Turkey is our Coalition partner and NATO ally. Therefore, Coalition forces in and around Manbij are not threatened by our partner and ally,” CJTF-OIR Public Affairs Officer Col. Thomas F. Veale told The Daily Beast on Tuesday.

“In relation to Turkey’s actions in Afrin: they are unilateral and not associated with Coalition operations in Syria. In accordance with an existing memorandum of understanding, Turkey is providing advance notification of its operations to the Coalition to ensure awareness prior to military actions,” he added.

But the rhetoric coming out of Ankara is not so bureaucratic, or conciliatory. The Turkish government has threatened U.S. troops that support Syrian Democratic Forces (SDF) in Manbij.

“Do not stand between us and the terrorists,” Turkish President Recep Tayyip Erdoğan said in a fiery speech on Jan. 15. “Otherwise, we will not be responsible for undesirable incidents which may occur. Take your own flags down from above the terrorists so that we are not forced to return them to you.” The Turkish Foreign Minister Mevlut Cavusoglu told reporters on Jan. 16 after meeting with his U.S. counterpart that the operation could be expanded to Manbij after the Turkish Afrin attack was finished.

“He is threatening Manbij as well—but before this happens the U.S should clarify its attitude towards its allies in the SDF,” Sinam Mohamad, a senior official in the local SDF-backed administration in northern Syria told The Daily Beast. And unlike the U.S., the Kurds see no difference between Afrin, Kobani, or Manbij.

“The SDF in al Jazeera [Hasakah province] is the same one as in Afrin. They defeated ISIS. Now the U.S. should stop Turkey from attacking Afrin? It is US responsibility,” Sinam Mohamad said.

“ The U.S. attitude is very weak. ” — Abdulkarim Omer with the YPG

After all, Kurds from Afrin also traveled to cities like Kobani and Raqqa under the SDF umbrella and fought ISIS, officials say.

“The United States should ask Turkey to stop this attack against the people; the international community should stop this war,” Mohamad said. “We in Syria want to end the war and to build stability and peace.”

Abdulkarim Omer, who deals with foreign relations for the Kurds in the Jazeera canton, told The Daily Beast that he was disappointed by the U.S. response. “The U.S. attitude is very weak,” said Omer. “It seems that America was aware of the agreement between Russia and Turkey amidst international and European silence.”

“Thousands of Kurdish forces... were killed fighting ISIS, and those that fought ISIS? Today they are being attacked by Turkey, which supports ISIS,” Omer said. He was alluding to the days when the Turkish frontier and airports seemed to be open not only to refugees fleeing Syria but to Islamic State recruits headed in—and terrorists headed out.

Omer noted that 300,000 internally displaced people (IDP) who fled the fighting between the Syrian regime and rebels live in Afrin. “But they live there now under Turkish airstrikes. The international forces must act and pressure Turkey and Erdoğan to stop this attack,” he said.

“The U.S. is telling the Syrian Kurds that Afrin should not expect American soldiers to play peacemaker for them,” Washington-based analyst Nicholas Heras, a fellow at the Center for a New American Security told The Daily Beast. “Only areas where the counter-ISIS mission is active, starting geographically in Manbij, will continue to be placed behind the shield wall of the U.S. military.

“The U.S. is telling the Kurds of Afrin that they chose to die on the hills of their homeland at their own peril and that they should cut any deals to protect Afin on their own accord,” said Heras. “Even more devastating, the U.S. is sending a not too subtle signal to Turkey that, at least in Afrin, the YPG is closer kin to the PKK, and therefore Turkey has a green light to continue Operation Olive Branch.

“Let’s be blunt,” said Heras, “the United States is horse trading Afrin to Turkey, hoping in exchange to receive Erdoğan’s restraint against the U.S. forces and the SDF in eastern Syria.”

But it’s not even sure that the Americans will protect Manbij against Turkey. Erdoğan can refer back to earlier U.S. promises that the Kurds should pull out from Manbij, as suggested by U.S. Vice President Joe Biden in a visit to Turkey in August 2016 during the Obama administration.

“In Manbij, if they break the promises, we will take the matter in our own hands until there are no terrorists left,” Erdoğan warned in a speech on Jan. 13.

“ Do not stand between us and the terrorists. ” — Turkish President Recep Tayyip Erdogan threatening the U.S.

Fresh in the minds of many Kurds is what happened in Iraq last year, when the Americans stood back and watched as Shia militias tied to Iran and Iraqi government troops rolled through contested areas in and around the city of Kirkuk that were claimed by the Kurds.

A senior Iraqi Kurdish official here in Erbil said the Americans might do something similar in Syria in the event of a Turkish attack on Manbij, telling the Kurds there, “It’s not your territory; we had a deal, pull out.” U.S. officials told CNN that Turkish-backed rebels already fired on patrols of U.S. forces in Manbij in the last few weeks. Moreover, U.S. officials told Reuters any Turkish operation in Manbij would be met with serious resistance and that Turkey promised not to expand their operation to Manbij.

Omar Aloush, a senior official in the new Raqqa administration, who maintains good contacts with the U.S.-led coalition and State Department officials, doubts Turkey will take Manbij. “I don’t believe it’s in the interest of other parties to give them this opportunity,” he said. “Turkey’s attempts to intervene in Syrian affairs are not a Turkish initiative, but the result of mutual understandings between mutual great powers of Syria with the goal to weaken local forces. Therefore, I doubt Russian or U.S. troops will be attacked,” he concluded.

In the meantime, the Kurds in Afrin are on their own.

—with additional reporting by Christopher Dickey