As early as the fourth century, Christendom experienced political and religious tensions between Western (Latin) and Eastern (Greek) styles of theology and governance. These differences were magnified by the East-West division officially declared in 1054, with many Eastern communities (Orthodox or “right-believing” Christians) proclaiming themselves formally independent of Rome. But the use of the term “Roman Catholic” came into common use after the sixteenth-century Protestant Reformation. Papal authority, an often contested issue for at least a millennium, again became a critical question. The reformers protested against the Church’s rigidly hierarchical structure, officially a kind of oligarchy but often in effect a monarchy in which the pope enjoyed greater power than the College of Cardinals.

The theological counterpart to the hierarchical system of internal governance were distinctively Roman teachings on the seven sacraments and on a vast multitiered celestial realm populated by saints and angels. Against these and other symbols of authority and mediated spiritual power, the reformers emphasized the priesthood of the faithful and the unmediated relationship of each believer to God. In response, Roman Catholicism further defined itself through the decrees of the Council of Trent (1545-1563) and the Catholic Reformation, spearheaded by the newly founded Society of Jesus or Jesuits (1540), among other emerging religious orders. Today Roman Catholics constitute about half the number of Christians worldwide.