US-backed forces are finally moving toward Raqqa, ISIS' de facto capital in Syria.
But the plan to retake the city and surrounding areas from the militants is burdened by a potentially fatal flaw: The alliance that is leading the effort on the ground, the Syrian Democratic Forces, is dominated by Kurdish fighters with the People's Protection Units, also known as the YPG.
Raqqa's population is mostly Arab, and residents of the city are wary of a Kurdish force potentially moving in to control it.
"People don't want the SDF to control the city because in general most of the people of Raqqa are not welcoming the YPG," Abu Ibrahim al-Raqqawi, an activist with the group Raqqa is Being Slaughtered Silently, told Business Insider.
"They say, 'At least if we stay under ISIS control and we keep our mouths closed and don't do anything bad, at least we can stay in our homes.' If the YPG controls our city, we cannot go back," said Raqqawi, who uses a pseudonym.
Raqqawi noted that the YPG had been accused of exiling Arabs from their homes in towns the Kurdish fighters had liberated from ISIS, which is also known as the Islamic State, ISIL, or Daesh.
But others say these concerns are overblown.
"I was in Tal Abyad (part of Raqqa province) today and yesterday, and Arabs tell me a different story," Wladimir van Wilgenburg, an analyst with The Jamestown Foundation who has been traveling with Kurdish forces, told Business Insider.
"According to people I spoke to," he added, "people of Raqqa don't care so much who liberates the city. As long as the city is not controlled by ISIS, and they'd rather have it as fast as possible."
So far, the SDF is focusing on territory surrounding Raqqa rather than on the city itself.
Before the alliance can move in on the city, however, it will need a proper contingent of Arab fighters. It's unclear where the appropriate number of fighters will come from or how long it will take to amass them, but the US recently dispatched special-operations forces to the area to recruit and train Arab fighters.
But the SDF might be Kurdish-dominated by design, as Sam Heller, a writer and analyst on Syria, said on Twitter. He pointed out that the "Arab, Raqqa-native component of the SDF seems to be too small and fragmented" to retake the city and that the YPG wants to keep that Arab force small and under its tutelage.
Raqqawi said Raqqa residents wanted fighters associated with the Free Syrian Army, a coalition group of rebels that aims to topple to government of Syrian President Bashar Assad.
"Most of the FSA is from the Syrian revolution," Raqqawi said.
Raqqa residents want the FSA "to be part of this — they don't want foreigners to control them," he continued, adding that Raqqa residents wouldn't consider the city "liberated" if it were done at the hands of Kurdish fighters.
"We can say 'controlling the city,'" Raqqawi said. "So people are saying, 'ISIS is controlling us,' or 'SDF is controlling us.' They are all foreigners, they are not from the city. People of Raqqa get tired of this."
Ryan Crocker, a career US ambassador who has worked across the Middle East including as the ambassador to Syria, told Business Insider that involving Kurdish forces in an offensive against Raqqa would be "dangerously counterproductive."
"Your average Sunni Arab would find it hard to choose between domination by Islamic State and domination by the Kurds," Crocker said. "The only way forward, in my view, is to increase a coherent, multifaceted effort to reach out to and work with the Sunni Arab forces that are not affiliated with Islamic State or with [Jabhat] al-Nusra," Al Qaeda's affiliate in Syria.
He later added: "Islamic State isn't going to be defeated by the Kurds. As a matter of fact, the Kurds will be a pretty good recruiting tool for them."
A Kurdish offensive on Raqqa could encourage some Sunni Arabs in the city to align with ISIS, which markets itself as a protector of Sunnis.
"People are going to the side of ISIS because they are thinking, 'At least they are Sunni Arabs,'" Raqqawi said.
Regardless of the ethnic and sectarian dynamics at play, the YPG have proved to be one of the most effective fighting forces against ISIS, and the US is short on other options for partnerships.
Crocker suggested groups like Ahrar al-Sham and Jaish al-Islam, but both have been associated with extremism.
Still, "we need to rethink" working with them, Crocker said.
"Neither of those two groups are going for a caliphate," he said, referring to the territory ISIS holds in Iraq and Syria. "Neither of them have a terror track record. Basically, I think the litmus test should be, if they'll work with us, we'll work with them."
Thomas Joscelyn, a senior fellow at the Foundation for the Defense of Democracies and an expert on Al Qaeda and its affiliates, cautioned against this kind of litmus test.
"Both Ahrar al-Sham and Jaish al-Islam are extremist organizations," he told Business Insider in an email. "Ahrar al-Sham's propaganda is openly jihadist. No one could possibly think it is anything but an extremist group."
Joscelyn noted that Jaish al-Islam had cooperated with Ahrar al-Sham and Jabhat al-Nusra at times as well.
And regardless of whether it's officially affiliated with either group, Joscelyn said, "Jaish al-Islam advocates an extremist version of Sunni Islam and is not moderate in any reasonable sense of the word."
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