Three Main Branches

There have been many divisions in the Christian Church over the centuries, some because of important differences, and others due to minor issues.

There are three basic branches of the Christian Church:

a. the Roman Catholic Church,
b. the Eastern Orthodox Church, and
c. the Protestant Church. 

These three branches resulted from two main divisions.

1. The first division of the Church came in 1054, when the Western Church with its base in Rome, and the Eastern Church, with its base in Constantinople, divided mainly over the question of the authority of the Pope in Rome. Another issue was the debate regarding the Holy Spirit. The Eastern Church (the Orthodox Church) did not want to include in the creeds the statement that the Holy Spirit proceeded also from the Son, and not only from the Father.

2. The second great division was the Reformation, which has as its key date the year 1517, when Martin Luther nailed his “Ninety Five Theses” to the church door in Wittenberg.

QUESTION:

What was the cause of the first main division in the Church?