Karl Paul Reinhold Niebuhr (June 21, 1892 - June 1, 1971) was a Protestant theologian best known for his study of the task of relating the Christian faith to the reality of modern politics and diplomacy. He is a crucial contributor to modern just war thinking. Wikipedia
D.B. Robertson, Love and Justice: Selections from the Shorter Writings of Reinhold Niebuhr (Cleveland, OH: The World Publishing Company, 1957). www.serve.com/thibodep/cr/niebuhr.htm
The definitive Wikipedia entry for Reinhold Niebuhr. Wikipedia is the biggest multilingual free-content encyclopedia on the Internet. en.wikipedia.org/wiki/Reinhold_Niebuhr