DAHUK, Iraq—Of all the many ancient peoples who once lived in the land between the Tigris and the Euphrates, Iraq's Assyrian Christians pride themselves on having persisted in their traditional homeland for millennia, even as other civilizations thrived then disappeared, as languages and cultures died out, as ethnic groups melted into the ways and genetic pools of their conquerors.

But today Iraq's Assyrians, and its Christians in general, fear that their place in this multiethnic, multisectarian mosaic society is shrinking, under severe threat from the ultraconservative Islamist group the Islamic State (IS).

It isn't the first time that Iraq's Christians have faced such a foe. The IS's earlier incarnation, al Qaeda in Iraq—a group that formed after the U.S.-led invasion in 2003—also menaced Christians, and others, prompting tens of thousands to flee into exile. (Read more about Arab Christians in "The Forgotten Faithful," a National Geographic feature story published in 2009.)

Now, the particularly harsh nature of the IS's assault on Christians, Yazidis, Shiite Muslims, and others who do not share allegiance to the IS's brand of ultraconservative Sunni Islam has led some of Iraq's Christians to take the unusual step of shedding their historical passivity and consider taking up arms to defend and eventually govern themselves. (Related: "Iraq Crisis: Ancient Hatreds Turning Into Modern Realities")

View Images Kurdish Peshmerga troops were on high alert around Badriyah on August 19, after the Mosul Dam was recaptured from IS forces. Some Christians are beginning to align themselves with the Peshmerga. Photograph by Gail Orenstein, NurPhoto/Sipa USA/AP

The Assyrian Patriotic Party, one of several Assyrian political organizations, has armed and dispatched a symbolic, rather than an active, force of some 40 members to join the Kurdish Peshmerga fighting the IS in the northwest of Iraq, according to party official Henry Sarkis.

The Peshmerga are the official forces of the Kurdistan Regional Government. It is the first such action by Iraqi Christians since some Christians fought briefly alongside the Kurds against Saddam Hussein.

Sarkis, 44, is the newly appointed branch chief of the party's office in Dahuk, a northern governorate in the semiautonomous Kurdish region that borders Syria and Turkey.

The 40 men constitute what Sarkis calls the "first wave," and the unit has adopted the name Dukha, an Assyrian word that means "sacrifice."

"We keep talking about Jesus and peace, and now we've reached the point where it's not enough," he said in an interview at his party's headquarters in Dahuk. "The age of waiting for the Peshmerga to take back territory while we sit is over. We took the decision that, with our limited abilities, we will try to participate."

The party bought weapons with money donated by members in the diaspora, Sarkis said, and is looking to raise more funds through donations to increase its stockpile.

Sarkis's men are mainly behind the front line, around the town of Sharfiyah, not so much fighting alongside the Peshmerga as holding territory the Kurdish forces have gained or are pushing forward from.

View Images Carved into a mountainside, the seventh-century Rabban Hormizd monastery overlooks the Nineveh Plains. Christians have lived in the area continuously since the first century, but in the past decade more than two-thirds of Iraq’s estimated 1.5 million have fled. Photograph by J.B. Russell, Panos

A Perilous Shift

Still, it marks a significant shift in the attitude of Iraq's Christians, a shift that's fraught with peril.

Since 2003, Iraq's Christian community has been viewed by other Iraqis as a passive victim of the country's many conflicts, not an active aggressor.

Taking up arms will make the Christians direct participants, armed targets who pose military rather than just ideological opposition to ultraconservative Islamist groups.

Sarkis acknowledges this but said his party is prepared to accept the consequences. "We're being killed in our homes, so why not defend ourselves? Then even if we die, we die with dignity," he said. "We didn't want to reach this point—we just want to live in our areas."

Before 2003, Iraq held about 1.5 million Christians. The number today is fewer than 500,000, say community leaders, the majority having been driven out by war and all the trouble it inflicts and breeds, including corruption and insecurity.

View Images Juan José Valdés, Daniela Santamarina, NG Staff. Source: INSTITUTE FOR THE STUDY OF WARS; ATLAS OF GLOBAL CHRISTIANITY 1910-2010, CENTER FOR THE STUDY OF CHRISTIANITY, 2009

According to the CIA's World Factbook, Shiites now make up 60 to 65 percent of Iraq's population, Sunnis 32 to 37 percent, and Christians just 0.8 percent. Most remaining Christians live on the Nineveh Plains, an area that is also home to other ethnic and religious minorities in Iraq, including the Yazidis and the Turkomans. (Related: "Iraq: 1,200 Years of Turbulent History in Five Maps")

Fall of Mosul

On June 10, Mosul, the capital of the Nineveh governorate, in northern Iraq, fell to IS-led militants in a blitzkrieg advance. The IS was ruthless with its enemies, uploading videos of mass executions of soldiers and security forces they'd captured. The Iraqi Army melted away, rather than try to repel the incursion.

Weeks later, the Kurdish Peshmerga also retreated from some areas in the face of an IS-led onslaught. Kurdish troops are now fighting, with the aid of limited U.S. air strikes, to regain territory.

The IS gave Mosul's estimated 8,000 to 10,000 Christians three options: convert to Islam, pay a tax, or die. Instead they fled en masse to villages on the Nineveh Plains, as well as farther north into the Kurdish heartland.

As few as 40 Christians remain in Mosul, according to Duraid Tobiya, 53, an Assyrian from the city and an adviser on minority affairs to the governor of Nineveh.

He said that the few who stayed were too sick, too old, or too poor to leave—so much so that the IS exempted them from paying the jizya, a tax on non-Muslims.

"I'm from Mosul—this is the first time I've been displaced," Tobiya said. "I lived through everything else that happened in Mosul, but it's all very different from what's happening now."

View Images Kurdish forces took up position against IS militias near Mosul on August 10. Several nearby towns, according to media reports, have fallen to the Islamist insurgents during the past week. Christian groups are now beginning to take the defense of their homeland into their own hands. Photograph by Mohammed Jalil, EPA

This time, he said, he had no faith in either the Iraqi Army or the Kurdish Peshmerga to protect Christians and other minorities, such as the Yazidis and Turkomans, against a much more dangerous foe, because both forces initially abrogated their duties.

Iraq's Christians, like all of the country's sectarian communities, do not speak with one voice. There are numerous political parties with varying platforms.

The solution as Tobiya saw it, was one of two options: "either mass emigration or an internationally protected safe zone. We have no other options. We are against emigration, because we are not only the sons of this country but its original inhabitants."

All dozen or so Christians interviewed by National Geographic adamantly shared the demand for a safe zone, akin to the two no-fly zones the West established in 1992 to protect Kurds in the north and Shiite Muslims in the south from the forces of former leader Saddam Hussein.

But 1992 was a long time ago in terms of Western resources and commitment to the region—especially at a time when President Barack Obama's administration is trying to pivot away from the troubles of the Middle East. Still, Tobiya and others insisted it's a viable option.

"We must protect ourselves—and also have international protection," he said.

View Images Refused entry to the humanitarian aid center in Al Hamdaniyah (Qaraqosh), a Christian refugee expresses his frustration to a Peshmerga soldier. Photograph by Vianney Le Caer, Pacific Press/LightRocket via Getty

Long-term Plans

In another part of Dahuk, behind the high concrete walls of the Assyrian Democratic Movement's headquarters, the local branch leader, Farid Yacoub, 42, says his party too is moving to arm its men.

It is registering volunteers, having gathered more than 2,000 names from the Dahuk governorate alone. But unlike Assyrian Patriotic Party leaders, Yacoub is recruiting men to protect Christian areas after they've been won back from the IS and its allies.

The intention is not to participate in the battle to reclaim those areas. "We have lots who are volunteering, who want to fight, but we don't have the means to arm them," he said.

The party doesn't want Christian villages such as Al Hamdaniyah (Qaraqosh) to be controlled or protected by the Peshmerga after they've been reclaimed. "Our people don't trust them any more," Yacoub said.

There's a bigger issue here. Nineveh has long been caught in a conflict between the central government in Baghdad and the semiautonomous Kurdish region in the north.

Some Christians on the Nineveh Plains have pushed to govern themselves, but Kurdistan also has claims on their territory and wants to absorb it into its zone.

Earlier this year, long before the country descended into the current level of mayhem and fragmentation, Baghdad "agreed in principle" to turn the Nineveh Plains, as well as two other areas, Fallujah and Tuzkhurmatu, into provinces. This would enable the Christians to manage their own affairs and secure an independent share of the national budget.

The Assyrian Democratic Movement doesn't want the Nineveh Plains to be part of Kurdistan, but Sarkis said his Assyrian Patriotic Party does.

Sarkis's men are working with the Peshmerga, independent of the national government's recent call for volunteers to fight the IS.

"Let's be honest," he said. "When the [Shiite-led] government asked for volunteers, it's because the war is sectarian, between Shiites and Sunnis. They didn't volunteer to protect Christians. They did so to fight Sunnis."

Yacoub, on the other hand, is not working with the Peshmerga and said his men are waiting for the central government to train and arm them, though with the proviso that they return to their areas.

"Our men said they were worried because they didn't want to defend areas other than theirs. We want to defend areas where our people are, specifically the Nineveh Plains," Yacoub said. "We're nationalists, but the circumstances that Iraq is living through now necessitate that we have a safe place, a place for us."

View Images A Kurdish policeman and a member of a local militia guard the entrance to Saint Yohana Church, in the Christian town of Al Hamdaniyah (Qaraqosh) on the Nineveh Plains. A few miles away is Mosul, the overwhelming majority of whose Christians have fled since the IS seized the city in early June. Photograph by J.B. Russell, Panos

Turning to Lebanon's Christians

Of all the dwindling Christian communities in the Middle East in recent times, only the Lebanese have picked up arms during civil turmoil. Lebanese Christians battled not only Muslims but also each other during their country's brutal 15-year civil war, which ended in 1990.

Duraid Tobiya, the adviser to the Nineveh governor, is also a member of Yacoub's Assyrian Democratic Movement. He said that since the fall of Mosul, his party had received a delegation from the Lebanese Forces, a militia turned political party, and had also sent representatives to Lebanon twice to meet with the party.

He didn't elaborate about the nature of the meetings, saying only that "we want to benefit from their experience. We explained our situation, and they explained their experience in Lebanon." He added, "We might proceed with some things, apply them on the ground."

Antoinette Geagea, a spokesperson for the Lebanese Forces in Beirut, confirmed the meetings. She said they were part of a series her party had undertaken with Christian spiritual and political leaders from Nineveh and Kurdistan, as well as Kurdish parties, in the wake of the fall of Mosul.

"There are many different views among Iraq's Christians," she said. "The Lebanese Forces told them that they must unite. We told them that if you all agree on a position, we will stand with you and help you."

That help could be political, in the form of lobbying international and regional players, or humanitarian. Or "if they want to protect themselves, we will put our experience at their disposal," Geagea said. "We told them they must decide on the best solution to help Christians stay in their country."

View Images On August 14, Christians and refugees from Mosul enjoyed a morale-boosting concert organized by the Kurdistan Regional Government at Saint Joseph Church, in the Ankawa suburb of Erbil. Fernando Filoni, a special representative of Pope Francis, also attended. Photograph by Feriq Ferec, Anadolu Agency/Getty Images

"We're Still Here"

Yaqoob Yaqo, one of the Assyrian Democratic Movement's members of parliament in Kurdistan, said that more than a hundred thousand Christians fled in the wake of the IS advances into their areas. "The problem is that even if [the IS] withdraws, a hundred thousand won't return."

He rattled off a long list of massacres and episodes of persecution directed against his people, but despite that litany, he wasn't downbeat.

"We're still here," he said, adding that his community has lived in these lands for 6,700 years, persisting after the fall of the Assyrian empire in 612 B.C. and practicing as Christians for the past 2,000 years.