The Orthodox Church in Ethiopia was founded by the monks Frumentius and Aedissius in the early fourth century, during the reign of King Ezana of Axum, who converted to Christianity along with many of his people. The two Syrian youths were found on a ship on the Axumite coast and taken to the king, who gave them a chance and employed them later on in the royal court. Frumentius eventually became the king’s secretary and treasurer and converted him to Chirstianity.
King Ezana later sent Frumentius to Alexandria with instructions to bring back a bishop from the Egyptian Coptic Church. Instead of an Egyptian bishop, the Patriarch of Alexandria decided that Frumentius himself would be more suited, since he knew the language and culture of Axum and had already converted many. So Frumentius became Ethiopias first archbishop; his ecclesiastical name being ‘Father of Peace´ and Christianity was declared the state religion.
In terms of doctrine, the Ethiopian Orthodox Church separated from the Coptic Church in the 5th century, because these still hold on to the Monophysite doctrine. While the Orthodox Church believes that Jesus had two distinct natures, one divine and one human, the Coptic Church believes that Jesus had only a divine nature in which the human nature was contained. The Ethiopian Church is in communion with the other Non-Caledonian Churches, namely the Coptic Church of Egypt, the Syrian Jacobite Church, the Armenian Apostolic Church and the Syrian Church of India. Coptic sacramental practices remain similar to orthodox ones, though they follow rather the Alexandrian rites rather than the Byzantine ones.
The Ethiopian church tradition has had its own interesting developments. Many practices related to ancient Judaism - such a representation of the Arc of the Covenant in every church - are unique to the Ethiopian Church.
Most of the Christian churches of the Middle East and the Mediterranean are Orthodox, rooted in the early Christian church, which’s liturgical and sacramental practices are unchanged in twenty centuries. The Patriarchate of Rome separated from the Eastern Churches in the eleventh century because of political and theological issues.
In the 1970s great strides have been made to try and heal the schism between the Orthodox and the Non-Caledonian Churches. The Coptic Patriarch of Alexandria accepted that Christ is fully human as well as divine - an important statement which opens up the dialogue for further steps. Representatives of the Patriarchate of Constantinople have recently visited the Ethiopian Church.
Today, even if not in direct canonical communion with the Orthodox of Greece, Constantinople, Russia, Ukraine, Antioch and other jurisdictions, the Ethiopian Orthodox Church is embraced fraternally, even to the extent that some of their priests are allowed to administer the sacraments in an Ethiopian church. It is not unusual for Ethiopian Orthodox to attend services at these other Orthodox churches.
Most of the "Ethiopian" or "Abyssinian" Churches in the USA have a Baptist or, in some cases, Pentecostal theological heritage and have no connection to the Ethiopian Orthodox Church. Their name reflects the fact that in past times 'Ethiopian' was often synonymous with 'African.'