Abstract
Christianity spread from Jerusalem in several directions. One of most powerful centers of Christianity was Rome, which became the seat of the popes, and remained so even after moving of the Emperor to newly-established (Greek at the time) Constantinople.
In addition to Rome closely associated with the apostle Peter, however, other large Christian communities existed, founded by other apostles. They were situated to the east of the Roman Empire and was known as the Churches, in common with the Roman one.
And so today, besides the largest Latin (Roman) Church, there are dozens of Eastern Churches that are justly pride on their own apostolic tradition. Their mutual communication and cooperation throughout history has been interrupted and re-established several times.
This development gave rise to present names united Churches (in the sense united with Rome) and Churches not united.