The Dr. King uses an allusion when he refers to the Reverend Reinhold Niebuhr, who is an American theologian and professor and also a leading intellectual during the mid-20th century. The reverend Niebuhr wrote several influential books and there was one that addressed the morality of the individual versus the immorality of the society. He is also credited with writing the Serenity Prayer. Dr. King writes "History is the long and tragic story of the fact that privileged groups seldom give up their privileges voluntarily."
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