At first glance, the authors of “American Grace” would seem to suffer from very bad timing. Between the completion of their manuscript and its publication, the dispute over the Islamic center in Lower Manhattan erupted, followed by the ­Koran-burning controversy, and somewhere along the way a New York cabdriver was stabbed, apparently for being a Muslim. All this gives a quaint air to their declaration, in the book’s first chapter, that “America peacefully combines a high degree of religious devotion with tremendous religious diversity.” And it seems to render moot one of their main goals: to illuminate the source of this inter­faith ­tolerance.

Actually, though, the story told in this book, by the social scientists Robert D. Putnam of Harvard and David E. Campbell of Notre Dame, is urgently relevant to the recent surge in interfaith tension.

True, America’s tradition of peaceful religious coexistence is largely about harmony among Christian denominations, and so doesn’t speak directly to the question of Islam’s place in America. But it’s also true that there was a time when many American Protestants viewed Roman Catholics no more charitably than a certain Pentecostal preacher in Florida views Muslims. In the 19th century, a Massachusetts convent was destroyed by anti-Catholic rioters, and civil unrest in Philadelphia — set off by rumors that Catholics wanted to rid the public schools of Bibles — led to some two dozen deaths and the destruction of two churches.

The question of how this changed, how Protestants came to stress their commonality with Catholics, is, generically speaking, the question of the day: How do mutual fear, hostility and suspicion give way to amity, or at least tolerance? How do supposedly deep doctrinal chasms recede from view? The answers offered by Putnam and Campbell deserve the attention of everyone concerned about America’s future cohesion.