Eastern Orthodox Church
The Orthodox Church as a single communion comprises nationally distinct autocephalous (self-governing) bodies united by a common theology. It is the second largest Christian communion after the Roman Catholic Church, with over 300 million adherents—around 13 percent of all Christians worldwide. The Orthodox Church holds itself to be the one, holy, catholic, and apostolic church established by Jesus of Nazareth and his apostles. The Great Schism of 1054 split Christianity between Orthodoxy in the East and Catholicism in the West. Orthodoxy believes that the Holy Spirit, like the Son, proceeds only from the Father instead of from the Father and the Son as in Western Christianity. Orthodoxy also rejects the primacy of the Bishop of Rome (the pope), instead holding that the Archbishop of Constantinople is the “first among equals.” The goal of the life of faith is theosis, understood as union with or likeness to God, giving Orthodoxy a more mystical nature than the rest of mainstream Christianity.
Orthodoxy is the dominant religious force across Eastern Europe, the Balkans, and Russia. Historically, Orthodoxy featured a close link between church and state. During this time, the rulers played significant roles in their respective national Churches until the rise and spread of militantly atheistic Soviet power across Orthodox lands in the first half of the twentieth century. The downfall of communism in 1991 has brought increased freedoms to national Orthodox churches. Many Orthodox churches today are seeking to fill the void left by the fall of communism through a revival of national faith. The autocephaly of national churches has long bred a tendency toward church-state unity, a desire many post-Communist Orthodox churches have pursued with varying success. Orthodoxy is also the largest Christian denomination in much of the Middle East, including Syria and Jordan. Because of its historical core around Constantinople (Istanbul), Orthodoxy has had a more sustained and extensive interaction with Islam than have either Catholicism or Protestantism on the whole.