Arianism
Arianism is a doctrine that came from Arius, a priest who taught in Alexandria. To many Christians, the teachings of Arianism are heretical and are not the correct Christian teachings as they deny that Jesus was of the same substance of the God of this monotheistic religion, making it one of the more prominent reasons Arianism has stopped being practiced today. Many may say and have claimed Arianism a powerful part of Christianity from the 4th to the 7th centuries AD however being against fundamental Christian Beliefs, such as that previously mentioned, this rhetoric was opposed by multiple theologians of the era as well as the early church (later Catholic Church).