QARAQOSH, Iraq -- Two years ago, Mubarak Tuwaya fled when Islamic State militants made a triumphant charge through northern Iraq. Now he is back in his hometown, wearing the uniform of an Iraqi militia that is helping drive out the extremists--and aiming to secure a place for Christians and other local minorities in Iraq's future. Capt. Tuwaya's U.S.-trained force is made up of about 500 troops and 300 unpaid volunteers, most of them Assyrian Christians from Hamdaniya, a district east of Mosul that is home to Qaraqosh, Iraq's largest Christian town. The Iraqi army's 9th Division captured the district with the militia's support in late October, in the early days of the current U.S-backed campaign to retake Mosul, the Sunni extremist group's last major stronghold in the country. The army then largely handed responsibility for holding Hamdaniya to the militia, whose next mission is to persuade other Christians it is safe to return. "This is the land of our fathers, we have to defend it," Capt. Tuwaya, a farmer and retired Iraqi army officer, said as he sat in the militia's makeshift headquarters, a former veterinary clinic, beneath the group's flag, a blue cross on a white background. Iraq's once sizable Christian population has dropped by as much as half since Saddam Hussein was ousted in 2003, to roughly half-a-million people today. When Islamic State seized swaths of Iraqi territory in 2014, more than 150,000 Christians fled their homes. Many of them lived in Hamdaniya, which is on the Nineveh Plain, a fertile region that inspired the militia's name: the Nineveh Plain Protection Units, or NPU. Members of the Christian community are now pressing the central government to grant Nineveh Plain the status of a province, a step intended to safeguard vulnerable minority groups, which also include Yazidis and ethnic Shabaks.

"It's a turning point in our history: to be or not to be in our homeland," said Yunadim Kanna, a Christian member of parliament in Baghdad. Militia leaders want the force to remain in charge of security in that territory even after Islamic State's defeat. The militia was formed in the fall of 2014 by displaced Christians who felt that Iraqi and Kurdish troops had abandoned them during Islamic State's advance. The militia was initially funded through donations. Members speak a modern version of Aramaic, the language of Jesus. The NPU reports to the central government, which earlier this year began paying for salaries and supplying assault rifles. The militia hopes to expand to around 1,000 troops and several hundred new recruits are currently in training. U.S. special operations forces helped train the militiamen over the summer, and recently supplied them with 200 rifles, machine guns and ammunition, said Capt. Tuwaya. A spokesman for the U.S.-led coalition against Islamic State didn't comment. The NPU's existence is a sign of the Christian minority's tenacity, and of how Islamic State's emergence deepened ethnic and religious fractures in Iraq, despite efforts to present a common front against the insurgency. Troops from the semiautonomous Kurdish region and Iran-backed Shiite militias are playing important roles in the campaign against Islamic State. But those groups have separate command structures, and the various armed forces are sometimes wary of one another.

Several NPU members said Iraqi Sunnis--many of whom initially supported Islamic State--wouldn't be welcome if they returned to the Nineveh Plain. The militia's capabilities are limited. Kurdish and U.S. forces had to intervene in May to repel Islamic State militants who attacked a town north of Mosul that the militia was holding, in a battle that left one U.S. Navy SEAL dead. And its members' methods can be raw. At a checkpoint outside Qaraqosh, one young militiaman boasted that he beheaded an Islamic State fighter with his pocketknife on his first day of combat. He showed a photo on his phone of the militant's head. Qaraqosh, where some 40,000 people once lived, is now a ghost town. The main street is littered with debris and charred furniture, the shops burned and their windows shattered. Airstrikes flattened buildings. The town's walls and churches are scrawled with depictions of Islamic State's black-and-white flag--and now also with graffiti of the NPU. "It's from this direction that we are expecting attacks," said Capt. Nimroud Moma, who commands a company of some 90 NPU militiamen, pointing out at the open desert toward territory still contested by Islamic State. Militiamen positioned heavy machine guns on the balconies of abandoned homes. Capt. Tuwaya said he joined the militia because he wants Iraqi Christians to return to their ancestral lands. Two of his six children have left Iraq, and the other family members share a two-bedroom apartment in Erbil. "I am doing this first for Iraq, and second for Hamdaniya," he said. After family members fled Qaraqosh, their house was looted and Islamic State militants moved in. When Capt. Tuwaya returned for the first time, in November, he said almost everything was gone. But he found a portrait of the Virgin Mary under a sofa, brushed off the broken glass and hung it back on the wall.