The indispensable Library of America, the most useful publishing venture in American letters, has produced an edition of Niebuhr’s major works, annotated by Niebuhr’s daughter, Elisabeth Sifton, a highly regarded editor and publisher. It belongs in the library of every student of U.S. foreign policy. Niebuhr, a Protestant pastor and theologian whose career stretched from World War I to the Vietnam era, was one of the United States’ keenest social thinkers. His approach to foreign policy, often known as “Christian realism,” was at bottom an attempt to bridge the gulf between the idealism promoted by American religious culture and the difficult choices that confronted a global superpower in an era of struggle against totalitarian regimes. For American thinkers such as George Kennan and Arthur Schlesinger, Jr.—to say nothing of President Barack Obama, whose 2009 Nobel Peace Prize acceptance speech was steeped in Niebuhrian thought—Niebuhr’s synthesis has offered an alternative to otherworldly idealism and cold-blooded Machiavellian realism.