What is ISIS?
It's an ambitious Sunni jihadist group that has fast become one of the world's most feared terrorist organizations. The Islamic State of Iraq and Syria, or ISIS, shot into the global spotlight in June when 800 of its fighters seized Iraq's second-largest city, Mosul, sending an estimated 30,000 Iraqi government soldiers fleeing and raising the specter of full-blown civil war. The militants now control an area roughly the size of Massachusetts, stretching from Syria's Mediterranean coast to the outskirts of Iraq's capital, Baghdad, and this week declared the creation of a caliphate, or Islamic state, on the territory. ISIS has imposed a brutal form of sharia law on its new subjects, and ruthlessly punishes locals who fail to adhere to its religious edicts with beheadings, crucifixions, and public floggings. "We no longer have to imagine a terror state," said Beirut-based political analyst Kamel Wazne. "We have one."

What are the group's origins?
ISIS grew out of al Qaeda in Iraq, the Sunni Islamist outfit that fought U.S. and Iraqi troops during the early years of the Iraq War. When the group was routed by Sunni moderates in 2008, its fighters reinvented themselves as ISIS and regrouped in neighboring Syria, where they seized territory during the chaotic uprising against President Bashar al-Assad. The withdrawal of American troops from Iraq in 2011 left another security vacuum, one ISIS has been able to exploit over the past year with the unintentional help of Iraq's Shiite Prime Minister Nouri al-Maliki. Following the U.S. departure, the Iraqi leader purged the government and security forces of Sunnis — who make up just over a third of the country's 33 million people. Alienated and angry, many Sunnis have supported ISIS in its fight against the Shiite-dominated central government. Maliki, says Michael Knights at the Washington Institute for Near East Policy, "played right into [ISIS's] hands."

How is ISIS funded?
The group pays the wages of its estimated 7,000 to 10,000 fighters — who include thousands of jihadists from North Africa and the Middle East, and at least 500 radicals from Europe and the U.S. — through an unlikely combination of organized crime and government activity. ISIS extorts local businesses, collects ransom payments, and loots state assets, as in Mosul, where jihadists stole $425 million from the city's central bank. Now that ISIS has established a secure, long-term stronghold in Syria's eastern province of Raqqa, the group is also able to make money through more conventional means: by taxing locals, and extracting up to 30,000 barrels a day from nearby oil fields, some of which it sells back to al-Assad's government. The group is believed to hold up to $2 billion in cash and assets, the kind of money that "allows them to start thinking bigger and broader" than a normal terrorist operation, said former deputy U.S. National Security Adviser Juan Zarate.

What does the group want?
To erase the borders in the Middle East and create a regional Sunni caliphate, an Islamic form of government that ended nearly 100 years ago with the fall of the Ottoman Empire. The beginnings of this proto-state can be seen in Raqqa, where ISIS runs social welfare programs, providing food and fuel to the poor, and even operates its own food standards board. Those services come at a heavy price. ISIS demands that women wear a niqab, or face veil, when out in public; smoking, alcohol, and music are banned; and locals must attend prayers five times a day. Thieves have their hands amputated, adulterers are publicly flogged, and government workers right down to local garbagemen have been summarily executed. "[ISIS] is bloodthirsty," a former ISIS member told Politico. "To them, killing a man is like drinking water."

Has that brutality backfired?
In some ways, yes. The group is considered so extreme that al Qaeda expelled the group in February, fearing its mass executions of civilians would turn Muslims against their Islamist cause. Some Western analysts believe that local Sunnis will eventually rise up and oust ISIS, which is what happened to al Qaeda in Iraq in 2008. "The one saving grace is that every affiliate has failed at running territory," a U.S. intelligence official told NBC News. "They alienate local populations every time."

Is ISIS a threat to the U.S.?
At the moment, the group seems more focused on securing its hold on its newly acquired territory than launching terrorist attacks against the U.S. But longer term, security analysts fear that Western extremists fighting with ISIS will return home and continue their bloody jihad. That might already be happening. The French-Algerian extremist Mehdi Nemmouche, accused of killing four people at a Jewish museum in Brussels last month, is believed to have spent a year fighting in Syria. When French police arrested him, they found a Kalashnikov wrapped in an ISIS flag. Right now, the territory controlled by ISIS "looks like a very extreme version of Afghanistan in the 1990s," says Zarate. "This is a cauldron of future terrorist threats to the West."

The new bin Laden
The leader of ISIS, Abu Bakr al-Baghdadi, is a man of mystery. Only two authenticated photos of the Iraqi militant exist, and he is rumored to wear a mask when meeting with anyone outside his inner circle, earning him the nickname "the invisible sheikh." A few facts, however, are known about the 43-year-old. He was held in a U.S. prison camp in Bucca, in southern Iraq, from 2005 to 2009, and within a few years of his release had become one of the world's most influential jihadist leaders. In fact, many Islamist extremists now consider al-Baghdadi, and not al Qaida's scholarly leader Ayman al-Zawahiri, the true heir to Osama bin Laden. "[Baghdadi] has captured cities, he has mobilized huge amounts of people, he is killing ruthlessly throughout Iraq and Syria," said former British foreign intelligence official Richard Barrett. If you were a jihadist who "wanted action, you would go with Baghdadi."