while, persecution, whether actual or only held over as a threat, became the most effectual barrier to reunion.
We have had abundant opportunities of observing how ecclesiastical, political, and doctrinal causes led to the total and final severance of the two great sections of the original Catholic Church. These we have seen in the clash of the rival claims of Rome and Constantinople; in the assumption of universal headship of the Church by the papacy, denied and repudiated in the East; in the crowning of Charles the Great by Leo iii., and the consequent severance of the Latin Church from the remnant of the Roman Empire which was identified with the Eastern Church; and lastly, in bitterly contested doctrinal differences, especially that connected with the Filioque clause added by the Western theologians to the Nicene Creed, and the miserable quarrel over the question of the use of unleavened bread in the communion, which seemed to outweigh all other occasions of conflict in the minds of the people of Constantinople.
Thus we have reached the stage when it will be no longer possible to carry on one continuous story of Church history. It will now be necessary to trace the history of each of the separate churches. In order to do this effectually we must go back to their origins, in the cases where these origins have not been considered already, and study them along the lines of their own distinctive courses of development.
