The Orthodox Church claims its legacy back to the '7 churches' in the Greek Mediterranean referred to in Revelation: Pergamon, Ephesus, Smyrna (now Izmir in Turkey), etc. which is going back about as far as you can go back. The split with the Bishop of Rome was mostly about political power. In the east, a Christian 'Roman' Emperor still existed, in the West the empire had collapsed into competing Christian and pagan nation states and the Roman Church wanted to have a unified, unquestionable ecclesiastical power to counterweight the loss of a unitary Christian political power, but Eastern bishops saw nothing special about their Roman brethren. By 1000 yrs into the history of the church there were doctrinal differences emerging between east and west, but those probably could have been papered over if not for the European church's political imperatives. Theological corruption in the service of political power in the Roman church in turn largely precipitated the Protestant reformation. The American evangelical movement has now set itself up for that same type of outcome.
What goes around, comes around.