What does President Lincoln mean when he says, "the last best hope of earth" during his State of the Union Address in 1862?

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Just think, why was it effective? -it appeled to critics because it was written well, that made it noticeable to the public including the white population-it was also recognizable to the african americans because it was about their heritage.-it was powerful just keep finding more points and elaborate on them. message me if you need more