The BibleThe Bible is the holy book of Christianity. It is considered to have the word of God by all Christians. Sometimes different churches disagree over exactly what the Bible means. There are many names for the Bible; some call it Holy Scripture, Holy Writ or the Good Book. The Bible was written long ago in Hebrew, Aramaic, and Greek, and translations were made later into Latin and some other languages. Now there are translations in many more languages, for example English.

Some traditions maintain other canons. The Ethiopian Orthodox Tewahedo Church maintains two canons, the Narrow Canon, itself larger than any Biblical canon outside Ethiopia, and the Broad Canon, which has even more books. The Latter-day Saints hold three additional books to be the inspired word of God: the Book of Mormon, the Doctrine and Covenants, and the Pearl of Great Price

In 391 Theodosius I established Nicene Christianity as the official and, except for Judaism, only legal religion in the Roman Empire. Later, as the political structure of the empire collapsed in the West, the Church assumed political and cultural roles previously held by the Roman aristocracy. Eremitic and Coenobitic monasticism developed, originating with the hermit St Anthony of Egypt around 300. With the avowed purpose of fleeing the world and its evils in contemptu mundi, the institution of monasticism would become a central part of the medieval world.

During the Migration Period of Late Antiquity, various Germanic peoples adopted Christianity. Meanwhile, as western political unity dissolved, the linguistic divide of the Empire between Latin-speaking West and the Greek-speaking East intensified. By the Middle Ages distinct forms of Latin and Greek Christianity increasingly separated until cultural differences and disciplinary disputes finally resulted in the Great Schism (conventionally dated to 1054), which formally divided Christendom into the Catholic west and the Orthodox east. Western Christianity in the Middle Ages was characterized by cooperation and conflict between the secular rulers and the Church under the Pope, and by the development of scholastic theology and philosophy.

Beginning in the 7th century, Christianity began a long series of conflicts with Islam as the latter faith quickly conquered areas of the Byzantine Empire, North Africa, and even southern Spain. Numerous military struggles followed, including the Crusades, the Spanish Reconquista, the Fall of Constantinople and the aggression of the Turks.

Martin LutherIn the early sixteenth century, increasing discontent with corruption and immorality among the clergy resulted in attempts to reform the Church and society. The Protestant Reformation began after Martin Luther published his 95 theses in 1517, whilst the Roman Catholic Church experienced internal renewal with the Counter-Reformation and the Council of Trent (1545-1563). During the following centuries, competition between Catholicism and Protestantism became deeply entangled with political struggles among European states. Meanwhile, partly from missionary zeal, but also under the impetus of colonial expansion by the European powers, Christianity spread to the Americas, Oceania, East Asia, and sub-Saharan Africa.

In the Modern Era, Christianity was confronted with various forms of skepticism and with certain modern political ideologies such as liberalism, nationalism, and socialism. This included the anti-clericalism of the French Revolution, the Spanish Civil War, and general hostility of Marxist movements, especially the Russian Revolution.