History of Christianity
The East-West Schism, or Great Schism, separated the Church into Western (Latin) and Eastern (Greek) branches, i.e. Western Catholicism and Eastern Orthodoxy.  It was the first major division since certain groups in the East rejected the decrees of the Council of Chalcedon (see Oriental Orthodoxy), and was far more significant.  Though normally dated to 1054, the East-West Schism was the result of an long time of disagreement between Latin and Greek Christendom over papal primacy and certain doctrinal matters like the filioque.  Bad feelings were intensified by cultural and linguistic differences.