Question Number 869:
What are the differences between the Orthodox, Coptic, and Tewahedo churches and why is there a split between them?
Orthodox is a generic term that can be applied to all Eastern and non-Roman Catholic Churches. There are two families of Orthodox Christians: the so-called "Eastern / Greek / Chalcedonian" Orthodox churches, and the "Oriental / Non-Chalcedonian" (sometimes called Pre-Chalcedonian or Monophysite) churches. The first group "Eastern Orthodox" accepts the teachings of the Council of Chalcedon of 451, the second does not, for complex reasons...
The Coptic, Armenian, Syriac-Jacobite and Tewahedo churches belong to the Oriental Orthodox family and they are in communion.
The split dates from 451, over the way the doctrine of the incarnation (hypostatic union) was formulated at Chalcedon, but the political / ethnic factors were and remain very important in this tragic split.
In many countries, Oriental Orthodox Christians can receive communion in Eastern Orthodox Churches, but the clergy cannot concelebrate. A lot of work has been done through dialogue to heal this schism, and several agreements have been signed. But it is very difficult to bring about a formal reunion because of the many practical problems, such as the anathemas (excommunications) pronounced in 451, the differences in the recognition of saints, the fact that two bishops occupy the same see in many places, etc.