This must be an American perspective (by a British author). Certainly in the UK different faiths get along pretty well, if you ignore the politicians, and money is in short supply. I suppose he has a book to sell, but it would be good if he had done any actual research.
Quite downplayed (in the review, anyway) is the bare-knuckled competitive approach of the two dominant religions. Spread not quite as much by the marketplace as success on the battlefields, large and small.