Bartilla, Iraq (CNN) -- On a dusty street corner in the Christian enclave of Bartilla, Iraq, Yousuf and his friends try to pretend that things are normal. They smoke, play dominoes and act like ISIS fighters aren't potentially just moments away from killing them. Bartilla is near Mosul, the first city to fall to the Islamic State in Iraq and Syria, an al Qaeda splinter group also known by its acronym ISIS. "We have all our bags ready. If anything happens, we will leave," said Yousuf. Others are determined to stay. "I might be the only girl left here. Everyone will go, but I will stay," said Mariana, 22, who spoke to CNN as she sat outside a church. "I won't leave my country." 'There won't be an Iraqi left' Religious minorities, such as Christians and Yazidis, make up less than 5% of Iraq's population. Since 2003, attacks against these minorities by insurgents and religious extremists have driven more than half of the minorities out of the country, according to the U.N. High Commissioner for Refugees. Those that remained sometimes took security into their own hands. After a series of attacks against churches in Baghdad in 2005, young men in Bartilla formed civilian defense units. Their efforts have intensified in recent weeks as militants have drawn near. The men won't let CNN film their checkpoints, or other defenses -- not with ISIS just a 10-minute drive away. Umm Shakir's brother and sister were killed in an explosion in Baghdad in 2008. She points at her son. "Everyday he pulls a 12-hour guard duty," she says. "It's very hard. If it stays like this, there won't be an Iraqi left in the country." 'This evil can't continue' Comprising mostly Sunni Muslims, ISIS wants to establish a caliphate, or Islamic state, that would stretch from Iraq into northern Syria. Since launching their offensive in Iraq, the group claims to have killed at least 1,700 Shiites. Hundreds of thousands of Iraqis have fled, prompting fears of a brewing humanitarian crisis. Most shops in Bartilla are closed. Their owners have either left or don't bother opening. Business is down; power is out. But Father Binham Lallou proudly points to the new renovations at his church -- the granite archways, the floor he always wanted to build. He remembers coming to the church as a boy. "What are we supposed to do?" he wonders out loud. "This is our land, our church that our ancestors built. This evil can't continue. A day will come when people will come to their senses."

CNN's Dana Ford contributed to this report.