Answer:
The Catholic Church split and reformed due to interpretation of doctrine. There were two capitals for the Catholic Church: Rome and Constantinople. This split--or the schism--divided the Catholic Church into the Roman Catholic Church and the Eastern Orthodox Church.
The doctrine causing the split was: The Eastern Orthodox Church did not want to follow the Pope, and they thought that Jesus and God were two different people (the filoque) The Roman Catholic Church believes that it should follow the Pope and that Jesus and God are one. They both thought that the Catholic Church should be based in its city.
This split led to a period of excommunication until Vatican II.
Another difference between the Churches is that the Eastern Orthodox Church focuses more on the senses during the mass and the pictures of biblical characters focus on the person; whereas, the Roman Catholic Church displays scenes from the bible. The Orthodox Church's Church is round (Like St. Basil's in Moscow), and Roman Catholic Church is straight until you reach the apse in the back of the Church (the altar, pulpit, etc... and behind).
Although the Churches are different, as far as I know, they both allow members of the other Catholic denomination to celebrate Mass and participate in the Eucharist.
Hope this helped!