By the second millennium, Christianity had spread to most of the Western world, Russia and Eastern Europe, the Middle East, parts of Africa, and had made some small inroads into the Far East as well. For the most part it had remained fairly unified in its fundamental beliefs with major theological disagreements being resolved in council. But as the millennium approached, certain major differences in theology and practice became increasingly troublesome. The fights between Rome and Constantinople led Pope Leo IX (1049-1054) and Patriarch Michael I to excommunicated each other.
The Great Schism (or Eastern Schism) of 1054 split the Church into Western and Eastern churches: the Western church gradually consolidated under the central authority of Rome, while the Eastern church adopted the name Orthodox to emphasize their commitment to preserving the traditions of the church and resistance to change. This Eastern Church refused to be consolidated under a single bishop, as this was completely alien to the structure the church had hitherto enjoyed. The Eastern Church recognized the Patriarch of Constantinople as the "First among equals" of the numerous bishops in charge of its autocephalous churches.
By the ed of the X century the papacy reached their lowest point. Papal elections, originally exercised by the citizens of Rome, had come under the control of the great noble families, among whom the Frangipani and Pierleone families and later the Orsini and the Colonna were the most powerful. Each of these would rather have torn Rome apart than allowed the other families to gain undue influence. They built fortresses in the city (often improvised transformations of the ancient palaces and theaters) and ruled Rome from them. From 932 to 954, Alberic II of Spoleto, a very able man, governed Rome firmly and restored its self-respect, but after his death and after the proceedings that accompanied the coronation of Otto I as emperor, Rome relapsed into chaos, and the papal dignity once more became the pawn of the emperors and of local feudatories. Contending factions often elected several popes at once.
The Pope Nicholas II (1058-1061) began a process to reconstitution of the Papal independence with respect to the imperial power. In addition to the diffusion of the ecclesiastical law, to become independent from the imperial one, he stated that the election of the popes is an exclusive right of the Cardinals (excluding the nobles in this way) and the election of other members of the clergy is an exclusive right of the Church (excluding the Emperor from this practice). Gregory VII (1073-1085) further fought the imperial abuses claiming the supremacy of the church over the municipality in 1075 (Dictatus Papae), being the power an expression of God. Emperor Henry IV took Rome in 1084 and the Pope he ended in exile. The Normans under Robert Guiscard came to rescue Gregory and thoroughly sacked the city on the same occasion (1084). A revolt of the Romans against the Normans forced the Pope to leave the city. The opposition of Church and Empire ended with the agreement signed in Worms between Henry V and Pope Calixtus II (1119-1124) in 1122, with the nomination of the bishops by the Church, and the granting of control over feuds by the Emperors.