This article should include material from Corpus Christianum

Christendom, in the widest sense, refers to Christianity as a territorial phenomenon: those countries where most people are Christians, or nominal Christians, are part of Christendom.

In a more significant and meaningful sense, it refers to the mediaeval and renaissance notion of the Christian world as a sort of social and political polity. In essence, the vision of Christendom is a vision of a Christian theocracy, a government devoted to the enforcement of Christian values, and whose institutions are suffused with Christian piety. In this vision, members of the Christian clergy wield plenty of political clout. Secular rulers are their subordinates and agents; and national or political divisions are subsumed under the unitary government of a unique and universal church institution. This tempting vision of an earthly crown was one of the greatest challenges to the institutional Christian church.

The seeds of Christendom were laid in A.D. 306, when Emperor Constantine became co-ruler of the Roman Empire. In 312 he converted to Christianity, and in 325 Christianity became the official religion of the Empire.

Christendom was given a firmer meaning with the creation of Charlemagne's kingdom, the Christian Empire of the West. On Christmas Day, A.D. 800, Charlemagne was crowned by the Pope as ruler of the Holy Roman Empire, a title which would exist up until Napoleon's defeat of Francis II in 1806.

After the collapse of Charlemagne's empire, Christendom became a collection of states loosely connected to the Holy See. Tensions between the popes and secular rulers ran high, as the pontiffs attempted to retain control over their temporal counterparts. The idea of Christendom was already greatly discredited by the time of the Rennaissance Popes because of the moral laxity of the pontiffs and their willingness to make war, peace, and alliances like secular rulers.

Christendom as a cohesive political unit effectively ended with the Reformation. Christendom can also refer to Christians considered as a group. The Christian World.

See also

• Caesaropapism
• Constantinian shift
• Dar al-Islam