The Yazidis are a ethnic minority in Iraq made up mostly of ethnic Kurds and isolated from the rest of the population due to their ancient beliefs. Best estimates put the group's worldwide membership at approximately 700,000 people and while they have members living in Sweden and Germany, the vast majority are in the Middle East.
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Members of the group believe in an ancient religion linked to Zoroastrianism and are considered “heretics” by radical Islamists.
This label has led to decades of persecution and now that ISIS has become more powerful in the region, they have targeted the group, forcing them out of their homes and into the mountains.
What do they believe in?
The group has been described as a sect due to their secretive nature, but that has also led to it being widely misunderstood.
Their belief system is thought to be a mix of different religions, including Christianity, Islam and Zoroastrianism, a Persian religion that was once the state religion in parts of ancient empires in what is now Iran.
Aspects of each of these religions can be seen in Yazidi practices, but they also have their own creations, including a fallen angel, referred to as the Peacock Angel. That figure, who is also known as Melek Tawwus, is one of seven main figures in their belief system and some outsiders - including both Muslims and Christians - see it as a case of devil worship.
The group has unique beliefs and customs steeped in their bloody history. Yazidis refuse to eat lettuce and despise the vegetable because a group of their people were slaughtered in lettuce fields in the 18th and 19th centuries. They also avoid wearing dark blue clothing, although there are alternating explanations for the decision: one being that the color is connected to the birth of the Peacock Angel, while another explanation is that Turkish army uniforms were blue during a different attack that left an estimated 100,000 Yazidis dead in the 1800s.
Have they been persecuted before?
Their controversial beliefs have caused them to be targeted for centuries.
Members of the group historically claim that they were attacked in 72 genocides in the 1700s and 1800s, but the violence didn't stop then.
In 2007, nearly 800 Yazidis were killed in a string of car bombs that went off in towns largely populated by their community.
What has ISIS done to them?
ISIS views Yazidis and Shiite Muslims as apostates and has been very vocal in their hopes of getting rid of the group.
ISIS, which now calls itself the Islamic State, issued an ultimatum to tens of thousands of Yazidis on Saturday to convert to Islam, pay a religious fine, flee their homes or face death.
Faced with the threats, about 50,000 Yazidis - half of them children, according to U.N. figures - fled to the nearby mountains, where they were running out of food and water.
What has been done to help them?
Cargo planes dropped parachuted crates of food and water over an area in the mountains outside Sinjar, where Yazidis where sheltering, according to witnesses in the militant-held town.
The Associated Press contributed to this report.