Christendom or the Christian world, in the widest sense, means Christianity as a territorial phenomenon. That means: those countries where most people are Christians and because of that are part of Christendom.
People have used the term Christendom for the medieval and Renaissance understanding of the Christian world as one single Body of Christ with Christ as the head. With the rise of Modernity and the Reformation during the early 16th century the understanding changed to a modern idea of a tolerant and diverse society that consists of many different communities.
- Marty, Martin E. The Christian World: A Global History. Modern Library chronicles, 29. New York: Modern Library, 2007.