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.
The first settlers came over from Europe by ship.
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Would send troops or weapons
The leading argument against slavery during this time in the US was simply that it was immoral, and went against God's will. Another was that it violated the Constitution, and yet another was that it was unsustainable in the South.