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There are two major causes: Germanic tribes moving into the Western roman Empire until its fall by Odacer in 476 A.D.. On the other hand, emperor Constantine I had chosen Byzantium, and ancient greek site, as the "New Rome", which would become Constantinople. Constantine I established Christianity as the official religion for the empire.The eastern half of the roman empire survived more than 1000 years, because of strategic location as a trading center and connection between Europe and Asia.
