Separation of Catholic and Orthodox Churches

The first real, although still partial, split came with the Nestorian
and Monophysite heresies condemned at the Councils of Ephesus
(431) and Chalcedon (451). A much more serious separation
occurred in 1054, when the Eastern churches and Rome mutually
excommunicated each other—ending recognition of the validity
of the other as a proper church. The two main issues involved
in this separation were the primacy of the pope and the manner
of explaining the doctrine of the Trinity. The Orthodox accepted
the pope as the most honored bishop of the Christian world, but
he was still one bishop among many. They thus did not believe
that the pope should have direct authority over all Christians.

The Orthodox Church also refused to accept the Catholic change
made to the Nicene/Constantinople Creed concerning the .
relationship of the Holy Spirit to the Father and the Son. For the Eastern
churches the Holy Spirit proceeds from the Father alone. The
Catholic Church declares that the Holy Spirit proceeds from the
Father and the Son, Jesus. The disagreements became so intense
that they led to the mutual excommunication of the patriarch of
Constantinople, the head of the Orthodox Church, and the papal
legate representing the power and authority of the pope as head
of the Western Church. The lengthy process of estrangement
continued until it culminated in a complete split upon the sack of
Orthodox Constantinople by the Catholic Crusaders in 1204