From here on, the entire medieval history of Europe is basically the history of the papacy and the empire. They were considered as the two arms of God for governing the church and the world. The papacy served as a wholesome check against military despotism of the emperors. The empire served as a check on the abuses of the papacy. Both secured order against the disintegrating tendencies of society. Both nourished the great idea of a commonwealth of nations, of a brotherhood of mankind, of a communion of saints. Nevertheless, the tendency of both was ultimately self-destructive.
The papacy grew in power and influence and the popes began to assert ever more blasphemous things of themselves – things, which the people, who had been pummeled into submission, accepted without question. Pope Innocent III (1198-1216) made “Vicar of Christ” the exclusive title of the pope, replacing older titles like “vicar of St. Peter.” Pope Boniface VIII (1294-1303) in his bull Unam Sanctum, declared that the salvation of every human depends upon obedience to him. He saw the pope as Christ on earth.
Four other things of note happened during this period. This first was the rise of Islam; the second was the Great Schism in 1054, third was the German mystic movement and lastly was the translation of the Bible into English by John Wickliffe.
Islam employed brutal techniques in proliferating the doctrines of Mohammed. Christianity made its conquest by peaceful missionaries and the power of persuasion. Islam conquered the fairest portions of the earth by the sword and cursed them by polygamy, slavery and desolation. In its conquering march Islam took forcible possession of the lands of the Bible, and the Greek church, seized the throne of Constantine, overran Spain, crossed the Pyrenees and for a long time threatened even the church of Rome and the German empire, until it was finally repulsed beneath the walls of Vienna. The Crusades, which figure so prominently in medieval Christianity originated in a desire to wrest the holy land from the followers of "the false prophet." Even the Reformation in the sixteenth century was complicated with the Turkish question, which occupied the attention of the diet of Augsburg as much as the Confession of the Evangelical princes and divines. Luther, in one of his most popular hymns, prays for deliverance from "the murdering Pope and Turk," as the two chief enemies of the gospel - (Erhalt uns,Herr, bei deinem Wort, Und steur’ des Papst’s und Türken Mord).
Viewed in its relation to the Eastern Church Islam was well-deserved divine punishment for the unfruitful speculations, bitter contentions, empty ceremonialism and virtual idolatry that degraded and disgraced the Christianity of the East after the fifth century.
No two churches in the world are at this day so much alike and yet so averse to each other as the Greek and Roman. They hold, as an inheritance from the patristic age, essentially the same body of doctrine, the same canons of discipline, the same form of worship. Yet their antagonism seems irreconcilable. The Greek and Latin churches were never organically united under one government, but differed considerably from the beginning in nationality, language and various ceremonies. These differences, however, did not interfere with the general harmony of faith and Christian life, nor prevent cooperation against common foes. As long and as far as the genuine spirit of Christianity directed them, the diversity was an element of strength to the common cause.
The doctrinal difference on the procession of the Holy Spirit existed before the Schism. However it assumed practical importance only in connection with the broader ecclesiastical and political conflict between the Patriarch of Constantinople and the Pope of Rome. The West did insert the filioque clause into the Creed without the East’s consent and without a Council, but the doctrinal issue was not as central as the two sides made it out to be. The West has continually denied that they mean to assert two First Principles into the Godhead. The East has continually asserted that this is what the West is doing. The East has been intransigent on this issue, even after demonstrations that the great Eastern theologians, such as Athanasius had taught the Dual Procession.
The first serious outbreak of this conflict took place after the middle of the 9th Century when Photius and Nicolas, two of the ablest representatives of the rival churches, came into collision. The dispute between them was at first personal. The deposition of Ignatius as patriarch of Constantinople, for rebuking the immorality of Caesar Bardas, and the election of Photius, then a mere layman in his place (858), were arbitrary and uncanonical acts that created a temporary schism in the East and prepared the way for a permanent schism between the East and the West. Photius was outraged by this conduct and held a counter-synod, and in turn deposed the successor of St. Peter in 867. In his Encyclical Letter to the Eastern patriarchs, he charged the whole Western church with heresy and schism and, most of all, for corrupting the Nicene Creed by the insertion of the filioque, and thereby introducing two principles into the Holy Trinity. This letter clearly indicates all the doctrinal and ritual differences that caused and perpetuated the schism to this day. The subsequent history is only a renewal of the same charges aggravated by the misfortunes of the Greek church and the arrogance and intolerance of old Rome.