The Great Schism in 1054 was the separation of the Eastern Orthodox Church from the Roman Catholic Church in the West. This division occurred due to differences between the two churches.
One irreconcilable difference was that they both had separate liturgies. The rituals were different and the Eastern Church used icons to represent saints and holy figures such as Jesus. There was also a language barrier. While in the East they used Greek, in the Western Catholic Church Latin was spoken.
However, probably the greatest animosity resulted from the fact that the Byzantine Church had a lesser status than then Western Church. Constantinople, the capital of the Byzantine Empire, declared that they were the new Rome, as they had been the remnant of the Old Roman Empire. But the West disagreed saying that Rome was fit to be the center of the Church because the city was founded by the Apostles.
The last straw to this intellectual battle came when the Patriarch of Constantinople, Michael Cerularius, ordered all Western churches in the East to be closed. Finally, in 1054 the two churches separated and have remained so ever since.