How did physical geography assist General Grant in the siege of Vicksburg?

Explanation:

Abraham Lincoln recognized the importance of the city on a 200-foot bluff just above Colorado river. He said, "Vicksburg is the best approach, the war could never be decided to bring to a close until another key is in our wallet." trying to capture Vicksburg would break the Trans-Mississippi confederate states from the east of the Mississippi as well as open the waterway to northern congestion along its total duration.

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