Muslim militias aren’t the only forces taking on the Islamic State group as it continues its spread across Iraq. Christians driven from their homes in Mosul by the fighting have also formed their own brigade, battling alongside anti-ISIS Muslim militias in hopes of exacting revenge and taking back their city.

"[They] displaced us from our houses, they took our money, killed our young men and women and they took our properties," the group's commander, Rayan Al-Kildani, told NBC News. "Therefore, Christians decided to fight the terrorists of ISIS."

The militia, about 1,000 men strong, calls itself the Bablyon Brigades. It is the only Christian formation within the Popular Mobilization Forces, which is an almost exclusively Shiite umbrella of brigades backed by the Iraqi and Iranian governments to fight ISIS. The Babylon Brigades formed in June 2014, immediately after Mosul, Iraq’s second-largest city, fell to the Sunni extremist group.

"ISIS terrorists do not differentiate among Christians, Muslims, Sunnis and Shiites – they kill everyone," Al-Kildani told NBC. "We have to help our Muslim brothers liberate Iraq."

Christians wanting to take up arms against ISIS, and lacking foriegn backers, are increasingly turning toward Shiite militias, as International Business Times reported from Lebanon earlier this year.

Fighters who spoke with NBC said Iraq had a strong history of religious coexistence – a peace that was brutally upended as ISIS pushed some 125,000 Christians from their homes in a 10-month span, according to CBS News. When ISIS took over Mosul, they demanded Christians convert, be subjected to a crippling tax or leave the city by foot. Subsequently, significant Christian artifacts, along with homes and businesses, were pillaged and destroyed.

For the first time in 2,000 years, there are no Christians left in Mosul, as the city became an early warning of what ISIS control would mean for other cities cross Iraq and Syria that would later fall to its forces. ISIS imposed a stringent interpretation of Islamic law and responded to dissent with harsh corporal punishment and execution.

"I found myself in a position to fight in order to restore what we lost," Yousef Hani Shamon, a 27-year-old Christian who fled the city by foot, told NBC. "ISIS terrorists are our enemy. They targeted our religion, and that is why I have to fight them."

This month, Shiite militias and the Iraqi military launched a counter-offensive to recapture Anbar province in the west from ISIS. Much of the fighting has focused on the outskirts of Fallujah, a strategically important city whose capture could signal a significant turning point for the anti-ISIS forces. It was unclear whether the Christian brigade was involved in any of the recent fighting in Anbar, a mainly Sunni region.