Catholicism.

There was only one church in western Europe from the death of Jesus until the Reformation; in fact, the term catholic means universal. After the fall of the Roman Empire the institution of the church was the one unifying force in a Europe fragmented into local fiefdoms. After the eastern branch separated in 1054, the western branch of the church became known as Roman Catholic because the bishop of Rome, or Pope, was considered to be Jesus' representative on earth and a successor to Peter, whom Jesus chose as the rock upon which the church was to be built. The Pope appointed bishops as the successors of the other apostles to oversee large dioceses, and they, in turn, appointed clergymen or priests to officiate in local parishes. Some clergymen were chosen by the Pope to serve as cardinals and advise him. Specialized orders arose...