ERBIL, Iraq — When fighters from the extremist Sunni groups led by the Islamic State of Iraq and al-Sham (ISIS) rolled into the northern Iraqi city of Mosul on June 10, Rami and his extended family in the al-Arabi neighborhood were rattled and frightened. Despite fears about what might happen to them under the victorious jihadists, they decided to stay, unlike many others who left.

“We, as Christians, were in Mosul for generations,” said Rami, now in the basement of the Um Nour Church in the Christian-dominated district of Ankawa, in northern Erbil, the capital of Iraqi Kurdistan. “Our ancestors lived there for hundreds of years. It wasn’t easy to leave.”

Their worst fears were for a while allayed, as the militants did not initially resort to scare tactics. Accounts by a number of recently displaced Christians paint a picture of a tactically tolerant Islamic State (IS) at the beginning, but gradually changing its behavior and adopting harsher practices.

“At first, the fighters said they had orders not to do anything against Christians,” said the 50-year-old Rami, sounding disappointed and angry. “They handed out green sheets containing their beliefs. They said they believed in Jesus as a prophet. … That way they made us feel safe, but then they deceived us.”