Some of the groups could not agree on certain points about Christian teaching (called “doctrine”) or practice. The first split was in the 5th century after the Church Council of Ephesus. The council agreed Nestorianism was wrong. The Assyrian Church of the East did not agree and split from the rest. The argument was about the nature of Jesus. Should he be regarded as God and human in one combined nature, or in two separate natures? Most of the bishops, following the Pope (the Bishop of Rome), refused to stay in communion with any bishop who would not say “two separate natures”. This was also discussed at the Council of Chalcedon, about 20 years later. The Christians who did not agree with the decision of the Council to excommunicate them, became the Non-Chalcedonian Orthodox. The largest Non-Chalcedonian Churches are the Coptic Orthodox in Egypt, the Ethiopian Orthodox, the Armenian, and some Lebanese Orthodox Churches. In general, these churches are known as Oriental Orthodox Churches. Recent discussions between the Roman Catholic Pope John Paul II and the Coptic Orthodox Pope Shenouda III concluded that they believe many of the same things after all, even though the Coptic Church does not recognise the Pope of Rome as its leader.
The third split happened in the 11th century. It is called the Great Schism. It was mostly based on personal disagreements between the Bishops of Rome and Constantinople. The disagreements were made worse because the two cultures often did not understand one another. Also, many Crusaders from Western Europe behaved badly. The Christians in Western Europe were led by the Bishop of Rome, known also as the Pope. They are called the Catholic Church. Most Christians in Eastern Europe, Russia, and the Middle East belong to the Orthodox Churches, led by the Bishops of other cities or areas.
In the 15th century the invention of the printing press made it easier for more people to read and study the Bible. This led many thinkers over the years to come up with new ideas and to break away from the Catholic Church. They started the Protestant or Reformed Churches. The most important Protestant leaders were Jan Hus, Martin Luther, and John Calvin. Later some of these groups disagreed amongst themselves so that these denominations split again into smaller groups. The main Protestant denominations today are the Baptist, Lutheran, and Calvinist Presbyterian Churches. In England, a similar protest against the Pope, first political and later religious, led to the Church of England which has bishops and officially calls itself Reformed Catholic but is often referred to as Protestant. The Anglican communion of churches includes several churches called “Episcopal” or “Episcopalian” because they have bishops. Some Anglican Churches have a style of worship that is closer to the Protestant services, others worship more like Catholics, but none of them accept the Pope, or are accepted by him. In general, the Protestant denominations differ from the Catholic and Orthodox Churches in having given up some of the traditional sacraments, having no ordained priesthood, and not having the same fondness for Mary, the mother of Jesus, that the Catholic and Orthodox churches have.
Groups have different ideas on the nature of God.
In the last two centuries, the rise of atheism and scientific challenges to the traditional Christian story of creation have caused some to believe in Creationism, as described in the Bible, and others to argue that the Bible is not literally true, but more like poetry.