nytimes.com | By Ben Hubbard and Eric Schmitt | May 12, 2019

RMEILAN, Syria — Dressed in camouflage and sipping tea, the Syrian commander who emerged as America’s closest ally in the battle that defeated Islamic State looked to an unsettling future.

The commander of the U.S.-backed Syrian Democratic Forces, who goes by the nom de guerre Mazlum Kobani, at a military base in Kurdish-controlled northeast Syria.CreditIvor Prickett for The New York Times

Soldiers attached to the Syrian Democratic Forces, checking IDs at a checkpoint on the outskirts of the northern city of Manbij.CreditIvor Prickett for The New York Times

Photographs commemorate the men and women from Kobani, a Kurdish Syrian town, who died in the fight against ISIS. CreditIvor Prickett for The New York Times

The commander, the Kurdish leader of the Syrian Democratic Forces, known by the nom de guerre Mazlum Kobani, praised his alliance with the United States in a rare interview recently and said he hoped American troops would stay in Syria.

But if they do not, he said, he is still fully prepared to defend his militia’s hard-fought gains during years of fighting the terrorist group.

“We were comrades in arms — we are on the same front fighting ISIS,” he said of the Americans, sitting in a furnished trailer in a compound that once belonged to the Syrian state oil company.

Now he is worried about a swift withdrawal, pointing to the American departure from Iraq in 2011, which was followed by the rise of Islamic State.

“They must not make the same mistake,” he warned.

As the commander of the American-backed militia that fought the Islamic State, Mazlum now oversees forces controlling one-third of Syria and sits at the nexus of clashing international interests in the jihadists’ former lands.

The Syrian government has threatened to take the territory back — by force, if necessary. Thousands of Islamic State fighters have gone underground to launch new attacks and plot their comeback.

And neighboring Turkey, which has fought Kurdish separatists at home for decades, is openly hostile to the Syrian Kurds along its border who have gained territory, sophisticated weapons and powerful alliances as a result of Syria’s eight-year civil war.

That puts Mazlum and the Kurdish forces that form the backbone of the S.D.F. at a crossroads. They have a historic militancy toward Turkey, but also an interest in preserving the power they have gained in Syria, said Dareen Khalifa, a senior Syria analyst with the International Crisis Group who has met with Mazlum in Syria.

Then there is the United States.

Mazlum owes most of his strength to the American presence in eastern Syria. But Washington’s commitment is uncertain and its plans have changed so frequently that no one — including him — knows how long the American forces will stay put.

“They have gained in Syria what they are not going to be able to get anywhere else,” Ms. Khalifa said of the S.D.F., “so they want to preserve that,” Ms. Khalifa said.

Those gains include a greatly expanded territory under their political control, where the group hopes to maintain its own administration.

So far, the United States has not used its relationship with Mazlum to push for a longer-term accommodation between Turkey and the Syrian Democratic Forces.

“The U.S. has refused to acknowledge the problem and therefore has refused to act on it,” Ms. Khalifa said.

An Essential American Ally

The partnership between Mazlum’s forces and the United States was born of necessity during a crisis.

In 2014, after seizing large parts of Syria and Iraq, the Islamic State surrounded the Kurdish town of Kobani in northern Syria, along the Turkish border. To fend off the assault, the United States armed the region’s main Syrian Kurdish militia while bombing heavily from the air.

The strategy worked, and the United States found a new partner in Syria, the Kurdish militia known as the People’s Protection Units, or Y.P.G. The militia was a Syrian offshoot of the Kurdistan Workers’ Party, or P.K.K., which has long fought for Kurdish autonomy in Turkey.

Unlike Syria’s Arab rebels, the Kurds were happy to fight the Islamic State instead of the Syrian government. And as a secular movement, they raised no concerns that they might harbor sympathies with Islamist extremists.

With backing from the United States and its allies, the group pushed the jihadists from other parts of Syria and built ties with other militias. In 2015, under prompting from the United States, it rebranded itself as the Syrian Democratic Forces — a mix of Kurdish, Arab and other fighters.

In the process, Mazlum became essential to the United States.

“We tend to go to Mazlum for everything,” said one American official who has worked with the militia leader. But the partnership suffered a blow in December when President Trump said he was withdrawing the 2,000 American troops from eastern Syria.

Since then, American plans have changed repeatedly, most recently calling for a drawdown to 1,000 troops followed by a reassessment. Mazlum said he hoped the United States would remain to help take on the Islamic State fighters who have gone underground and to oversee a restructuring of the S.D.F. into an internal security force.

But he will have to reckon with his immediate neighbors, especially if the United States leaves. Negotiations with the Syrian government about reuniting the northeast with the rest of the country have gone nowhere, he said, and the Trump administration has discouraged further talks.

And the more powerful Mazlum’s forces get, the more they scare Turkey, which has threatened to send troops across the border to get rid of what it considers a growing security threat. Meanwhile, Kurdish fighters have dug extensive tunnels near the border to fight back in case the Turks attack.

Mazlum said that he needed more support from the United States-led coalition, not less, but that his forces would survive regardless.

“Of course it will be hard,” he said. “But if we end up on our own, we’ll continue the war as we did in the time before the coalition.”

Two Radically Different Views of the Same Person

Mazlum Kobani, who is 52, remains a mysterious figure, with basic facts about him subject to debate, including his real name. When asked directly, he acknowledged that he that he had been a longtime member of the P.K.K., which the United States and Turkey consider a terrorist organization.

That is history, he said.

“The Turks are focused on the period before 2011,” he said, “but we are looking ahead.”

He offered only snippets about his background, saying he was arrested repeatedly by the Syrian government and later went to Europe for “political work,” followed by “military work” in Iraq.

Officials from the United States and Turkey speak about him as if describing two different people.

“He is a very educated, savvy politician and a very effective front-line soldier,” said another American official who has worked with Mazlum. “He is the head of a highly disciplined and, to some degree, ideological movement that is centrally controlled and has a long history of fighting.”

Turkey focuses on that history. Officials in the Turkish Foreign Ministry provided documents about his background, which included overseeing an armed wing that launched deadly attacks on Turkish security forces. Officials in Iraq provided similar details.

Can Acun, a researcher with SETA, a pro-government think tank in Turkey, said Mazlum’s history raised concerns that his forces could use Syria as a base for future attacks on Turkey. The fact that he was supported by the United States, Turkey’s NATO ally, only made it worse.

“Turkey doesn’t want northeast Syria to become a safe zone for the P.K.K.,” Mr. Acun said.

More than a half-dozen American officials who have worked with Mazlum acknowledged his ties to the P.K.K. “Life is complicated in the Middle East,” the second United States official said.

He said joining forces with Mazlum had been necessary to fight the Islamic State, which was the overwhelming American interest in Syria.

“We owe these guys a lot,” he said. “And they owe us a lot.”

Ben Hubbard reported from Rmeilan, and Eric Schmitt from Washington.