History of the East–West Schism
Disunion in the Roman Empire further contributed to disunion in the Church. The Emperor Diocletian famously divided the administration of the eastern and western portions of the Empire in the early 4th century, though subsequent leaders (including Constantine) aspired to and sometimes gained control of both regions. Theodosius the Great, who established Nicene Christianity as the official religion of the Roman Empire (see Edict of Thessalonica), was the last Emperor to rule over a united Roman Empire. Following his death in 395, the division into western and eastern halves, each for a few decades still under its own Emperor, was never reunited.
Persecution of pagans in the late Roman Empire
In 476, the last western emperor, Romulus Augustulus, was deposed by Odoacer, who became the first "barbarian" king of Italy. Pagans used the occasion to attempt to revive the old rites. In 484, the Magister militum per Orientem, Illus, revolted against Eastern Emperor Zeno and raised his own candidate, Leontius, to the throne. Leontius hoped to reopen the temples and restore the ancient ceremonies; as such, many Pagans joined in his revolt against Zeno. Illus and Leontius were compelled, however, to flee to a remote Isaurian fortress, where Zeno besieged them for four years. Zeno finally captured them in 488 and promptly had them executed. Following the revolt, Zeno instituted harsh anti-paganism policies. With the failure of the revolt of Leontios, some pagans became disillusioned and became Christian, or pretended to do so, in order to avoid persecution. The subjugation of the Roman Empire to Christianity became complete when the emperor Anastasius I, who came to the throne in 491, was required to sign a written declaration of orthodoxy before his coronation.