What advantage did the byzantine empire have that enabled it to survive as a political entity for a thousand years longer than the western part of the roman empire?

Byzantine Empire was able to survive for thousands of years longer than the western part of the Roman Empire because of its strong military force. The Byzantine military was able to remain stronger by fighting with its neighboring territories invaders by organizing army with trained and well equipped in the world. The empire began to expand largely through conquest. The basic role was to defend against enemies. The Byzantine Empire formed a professional standing army with heavy cavalry, archers and infantry.      

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