Since the spread of Christianity from the Levant to Europe and North Africa during the early Roman Empire, Christendom has been divided in the pre-existing Greek East and Latin West. Consequently, different versions of the Christian religion arose with their own beliefs and practices, centred around the cities of Rome (Western Christianity, whose community was called Western or Latin Christendom) and Constantinople (Eastern Christianity, whose community was called Eastern Christendom). From the 11th to 13th centuries, Latin Christendom rose to the central role of the Western world.
In its historical sense, the term usually refers to the Middle Ages and to the Early Modern period during which the Christian world represented a geopolitical power that was juxtaposed with both the pagan and especially the Muslim world. In the traditional Roman Catholic sense of the word, it refers to the sum total of nations in which the Catholic Church is the established religion of the state or to those with ecclesiastical concordats with the Holy See.
The Anglo-Saxon term cristendom appears to have been invented in the 9th century by a scribe somewhere in southern England, possibly at the court of king Alfred the Great of Wessex. The scribe was translating Paulus Orosius' book History Against the Pagans (c. 416) and in need for a term to express the concept of the universal culture focused on Jesus Christ. It had the sense now taken by Christianity (as is still the case with the cognate Dutch christendom , where it denotes mostly the religion itself, just like the German Christentum).
The current sense of the word of "lands where Christianity is the dominant religion" emerged in Late Middle English (by c. 1400). This semantic development happened independently in the languages of late medieval Europe, which leads to the confusing semantics of English Christendom equalling German Christenheit, Dutch christenheid, French chrétienté vs. English Christianity equalling German Christentum, Dutch christendom, French christianisme. The reason is the increasing fragmentation of Western Christianity at that time both theologically and politically. "Christendom" as a geopolitical term is thus meaningful in the context of the Middle Ages, and arguably during the European wars of religion and the Ottoman wars in Europe.
Canadian theology professor Douglas John Hall stated (1997) that "Christendom" means literally the dominion or sovereignty of the Christian religion." Thomas John Curry, Roman Catholic auxiliary bishop of Los Angeles, defined (2001) Christendom as "the system dating from the fourth century by which governments upheld and promoted Christianity." Curry states that the end of Christendom came about because modern governments refused to "uphold the teachings, customs, ethos, and practice of Christianity." British church historian Diarmaid MacCulloch described (2010) Christendom as "the union between Christianity and secular power."