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the rich merchants of Mecca thought that Muhammad was danger ,consequently ,he moved to Medina in 622 This date is known as the hegira , and marks the start of the Muslim calendar
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The eastern Roman Empire was richer than the western Roman empire, and it resisted the Germanic invasions.
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germanic tribes lived to the north of the roman empire. The romans called them barbarians (foreigners) The empire´s wealth and military weakness led to a series of Germanic migrations across the frontier.
