The Battle Hymn of the Republic is one of the most recognisable songs in the world. Easy to sing, and to march to, its words are stirring and optimistic, and filled with vivid images: trumpets that never call retreat, watch-fires of a hundred circling camps, trampling of the grapes of wrath, loosing of the fateful lightning of the terrible swift sword, burnished rows of steel, lilies in whose beauty Christ was born across the sea. It contains the frisson of redemptive violence, too: as he died to make men holy, let us die to make men free. It is, in fact, the most perfect musical expression of the idea that America is peculiarly blessed by God -- the last best hope of earth. Adam talks to John Stauffer and Richard Carwardine to find out more about the song's origins.