Donatism was a sect of early Christianity which emerged in Carthage, North Africa during the 4th century AD, existing until the 6th century. Bishop Donatus Magnus believed that any priest or bishop who had betrayed the Christian Church during Diocletian's persecutions had to be rebaptized and reordained in order to regain his authority to celebrate the sacraments and perform other priestly or episcopal duties. Donatus believed that sacraments performed by apostate clergy were invalid, but followers of mainstream Christianity believed that judging the validity of the sacraments based on the moral worthiness of the priest would make it impossible for the recipient of a sacrament to know if it was valid. Augustine of Hippo campaigned against Donatism as bishop, but it survived the Arian persecution under the Vandals, as well as the Byzantines' reconquest of North Africa. However, it disappeared during the 500s, and its split with mainstream Christianity led to the weakening of the faith ahead of the Islamic conquests of the 600s.
Had it survived to this day, it would have been the main Christian denomination of the modern-day country of Tunisia which is predominantly Sunni Muslim.