History of the Roman Empire
Theodosius was the last Emperor who ruled over the whole Empire. After his death in 395, he gave the two halves of the Empire to his two sons Arcadius and Honorius; Arcadius became ruler in the East, with his capital in Constantinople, and Honorius became ruler in the West, with his capital in Milan and later Ravenna. The Roman state would continue to have two different emperors with different seats of power throughout the 5th century, though the Eastern Romans considered themselves to be the only ones who were fully Roman. Latin was used in official writings as much as, if not more than, Greek and the two halves were nominally, culturally and historically, if not politically, the same state.
East–West Schism
In 476, when the last emperor of the western part of the Roman Empire was deposed and the western imperial insignia were sent to Constantinople, there was once again a single Roman Emperor. However, he had little power in the West, which was ruled almost entirely by various Germanic tribes. In the opinion of Randall R. Cloud, the permanent separation of the Greek East from the Latin West was "the fundamental reason for the estrangement that soon followed between the Greek and the Latin Christians".