The reasons for the Great Schism are: 1. Disagreement over who was the head of the church; and 3. Disagreement over the language in which to perform the rites.
The Great Schism (also known as East–West Schism) was the break of communion between Roman Catholic Church and Eastern Orthodox churches (centers of East and West side of the Great Roman Empire) in 1054. The main disagreement was over who was the head of the church, for the Pope wanted to be above the Patriarch. The other disagreement was over the language when performing rites (liturgies). The Catholic Church recognized only Latin as the sacred language for rites, but the Orthodox Church performed liturgies in Greek. This disagreement later happened inside of the Catholic Church when the Martin Luther translated "Bible" to German, which resulted in creation of Protestantism.