You're question is a little unclear and could mean two things so I'll answer both.
Why did the Orthodox denomination emerge?
The Orthodox emerged when the eastern and western bishops excommunicated each other in a power struggle in 1054. The east became the Orthodox and the west became the Catholics.
Who broke off from the Orthodox?
There was no reformation in the east like there was in the west. There was the separation of the Coptics, but that was simply on their slightly different belief about the nature of the Trinity.
No. No Eastern Orthodox denomination (Greek, Russian, etc.) performs such marriages.
Eastern Orthodoxy is a Christian denomination (the second largest, with Catholicism first). So Orthodox Christians believe in the Holy Trinity and that Jesus Christ is the Son of God.
Eastern Orthodoxy is a Christian denomination (the second largest in fact). Therefore, they have the same commandments as any other Christian denomination- the 10 Commandments given to Moses.
catholicism
Greek Orthodox is a denomination in Christianity.
The majority religion in Bulgaria is Protestant Christianity-- the Bulgarian Orthodox Church is the most dominant denomination, but there are some Catholics, Jews, and Muslims who live in Bulgaria too.
They are called Eastern Orthodox Christians or just Orthodox Christians.
Eastern Orthodox is a branch of Christianity.
The Orthodox Church is not a denomination. The Orthodox Church is the original Christian church, founded by Jesus Christ and His apostles. "Denominations" are the Christian groups which trace their histories back to splitting off from the Orthodox faith.
No, the Greek Orthodox church is a part of the Eastern Orthodox Churches.
Orthodox is one such Baha'i denomination.
Yes, the Lutheran denomination is generally considered to be orthodox in its beliefs and practices, adhering to traditional Christian teachings and doctrines.