Last week, tens of thousands of Yazidis fled from the northern Iraqi town of Sinjar into nearby mountains, escaping violence from the Sunni militant group that calls itself the Islamic State of Iraq and Syria, or ISIS. Their plight—stranded, and dying of hunger and thirst—prompted the United States to conduct airstrikes against ISIS, in the first major U.S. military push in Iraq since 2011. Suddenly, international attention has turned to this tiny faith group, whose estimated population ranges from 300,000 worldwide to 700,000 in northern Iraq lone.

Western media outlets have focused on the idiosyncrasies of the faith, like adherents' supposed fear of lettuce and pumpkins, and refusal to wear the color blue. And supposedly, the religion is syncretic, meaning that it incorporates elements of many different faith traditions, including Christianity, Islam, and Zoroastrianism.

Philip Kreyenbroek, a professor at Germany's University of Göttingen who has written several books on Yazidis, says these characterizations of the religion are only partially true. "They have very ancient roots," he noted. Although it's difficult to determine exactly how old the religion is, scholars believe the Yazidis were one of the Indo-European peoples who lived in ancient Mesopotamia. Around 3,000 B.C.E, when other groups migrated east to India and Iran, the ancestors of the Yazidis stayed and settled in the area now known as Kurdistan.

Although "they believe in an absolute god who is responsible for everything that happens in the world, good or evil," which in some ways resembles the Abrahamic conception of God, their faith is actually rooted in an older tradition: "Basically what they believe is in a much older divinity called Mithras," an ancient Indian and Iranian god, Kreyenbroek said. Yazidis also believe the world is guarded by seven angels, the most important being Melek Taus, or the peacock angel.

Starting in the 11th century, these ancient beliefs took on new forms. "Some say these messages became less comprehensible in the 11th century, when a Sufi mystic sought solitude in the mountains [of northern Iraq]. He was so charismatic that all these people who followed non-Islamic religions followed him," Kreyenbroek explained. This was Sheikh Adi ibn Musafir, a practitioner of mystical Islam, whom the Yazidis venerate as a holy figure.

The Yazidis began "using Islamic words and concepts to refer to their ancient beliefs," Kreyenbroek said. They also practice rites like baptism in water, which may or may not be drawn from cultural encounters with early Christians. But these overlaps are largely superficial—Muslims don't consider Yazidis to be a "people of the book," or one of the Abrahamic religions of Christianity, Judaism, and Islam.

The Yazidis also hold many beliefs that aren't found in Abrahamic religions. "They shouldn't wear the color blue," said Kreyenbroek. "Some people say they can’t eat fish, a lot of people say they can’t eat lettuce, and some people say pumpkins as well.” But most people don't follow these rules strictly, he added—they're mostly limited to priests, or perhaps more orthodox Yazidis like those who live in Sinjar.

The origins of these beliefs are unclear. “The word for lettuce, for instance, in Arabic—the Kurds don’t speak Arabic, naturally—but when they speak Arabic, they don’t differentiate sounds, and the word for cursing, which is taboo, and the word for lettuce, are very similar. I’ve always suspected that this has something to do with it,” Kreyenbroek said. Others have linked this belief to the 13th-century execution of a Yazidi saint, who was pummeled with lettuce. (It's worth noting that Kreyenbroek is one of the few scholars in the world who studies the Yazidis, but he still went out of his way to say that a lot is unknown about the faith. Even as the ancient religion faces extinction, we still don't understand it very well.)

Since Yazidis are not a "people of the book," "they [are] not protected in Islamic law," Kreyenbroek pointed out. And "they [are] thought to be devil worshipers—and there is nothing as horrible and unclean as devil worshipers."

This is why ISIS is so intent on eliminating the group—and why the international community is so concerned about a genocide against them, said Birgül Açıkyıldız Şengül, a professor at Turkey's Artuklu University who studies Yazidi art and culture. "It’s not the same as ... with the Christians or the Shia Muslims," she said. The Yazidis "are not considered a religion."

That's not to say that ISIS isn't targeting Iraq's Christians and majority Shiite Muslims. Other religious minorities in northern Iraq, including the Kaka'is, a sister religion of Yazidism, and the Shabak, a cultural group that has some distinctive religious qualities, are also in the jihadist group's crosshairs. Instead of fleeing, some of these groups have chosen a different path: hiding. "Kaka'is are sometimes saying they're Shiites," Kreyenbroek said.

But the persecution of Yazidis in recent weeks has been particularly acute, and it's in keeping with the sect's long history. In fact, suffering has become an integral part of the group's self-narrative. "The Yazidis say they were persecuted 72 times in the past, but we don’t know. We don’t have sources until the 13th century," Şengül said. “The Yazidis became very strong in the 13th century … in northern Iraq to northern Mesopotamia, Turkish-tied Iran, and even Syria. At the same time Islam was becoming very strong in the region, so Muslim leaders started to persecute them.”

During the Ottoman era, the Yazidis faced pressure to convert to Islam, according to one 19th-century text. Some believe this is the origin of the symbolic number "72," representing the number of massacres committed by Ottoman caliphs. But again, as Şengül said, "we don't know."

In the 20th century, under former Iraqi President Saddam Hussein, the Yazidis faced killings and relocations because they are ethnic Kurds. "[They] were forced to take part in the war against Iran, and they were always sent to the front—they were the first to die," Kreyenbroek said.

Over time, these experiences have driven Yazidis to separate themselves from Iraq's Muslim communities. "This memory, the bad memories of being persecuted by Muslim leaders—it’s a reaction, a way of protecting themselves," Şengül said.

"They believe, as the Jewish people believe, that there’s a historic tendency to persecute them," Kreyenbroek observed.

This instinct to self-isolate may have contributed to the dire situation in Sinjar. "The Kurdish area in the Middle East is a mountainous area in general—and mountains protect people when they are attacked by outsiders," Şengül said. When faced with the threat of death at the hands of ISIS, the Yazidis fled to higher ground.

Now they're also fleeing from other areas of northern Iraq. In addition to the Sinjar region, many live around Dohuk, in Kurdistan. Şengül said her town in Turkey, Mardin, is seeing an influx of refugees, and others are heading to Syria. She's heard of at least three children who died on the Turkish border, waiting to cross from Iraq.

These forced migrations may further alter Yazidi identity. "They identify very, very strongly with the land," Kreyenbroek said. "The Valley of Lalish, that’s the heart of the Yazidi. It’s on the borderline of the Kurdish autonomous region, and [it's the location of] the sanctuaries of the various holy people, of the angels."

Here, "they’ve always felt secure. Sinjar, until recently, was talking about the possibility of establishing a Yazidi republic. I thought this was nonsense," he added, "but among the diaspora, it was quite seriously discussed."

The Yazidi population is heavily concentrated in Iraq, but there is a something of a diaspora in other countries—although it's impossible to know how big it is. Kreyenbroek spoke of communities in Germany, Turkey, and Holland; roughly 200 families live in the United States, half of them in Nebraska. Recently, Yazidis in Armenia tried to establish themselves as an independent, non-Kurdish ethnic group for political reasons—Armenians are still wary of Kurdish Muslims because of memories of the ethnic cleansing of Armenians that took place during World War I.

Even so, among Yazidis, "there is a very close link with the land," said Kreyenbroek. "It's very difficult for people to give it up, to reinvent their religion without the physical presence of sanctuaries and holy wells and holy groves."

Now, "the fear is that the ISIS is so close, and the first thing they would do is to destroy this holy site," Kreyenbroek said. "When that goes, that’s virtually the end of this religion."