“Christians were contractually obliged to pay the jizya, or minority tax, which in Islamic Sharia law is the amount of money paid by non-Muslims or ‘dhimmis’ in exchange for protection.”
That is straight from the Qur’an: “Fight those who believe not in Allah and the Last Day and do not forbid what Allah and His Messenger have forbidden, and do not practice the religion of truth, even if they are of the People of the Book — until they pay the jizya with willing submission and feel themselves subdued.” (9:29)
“Christians living under ISIS are not permitted to build any new churches, religious facilities, nor are they allowed to repair existing ones, cannot publicly show any crosses, pray or recite the Bible in public, are prohibited from any acts of aggression against the Islamic State, are forbidden from stopping the conversion of any Christian to the religion of Islam and cannot sell pork products or alcohol to any Muslims nor consume these products, forbidden in Islam, in public.”