In this article, I consider the absence of a general readership of William Blake's poetry in nineteenth-century Britain and compare that neglect to the American Transcendentalists' reading of Songs of Innocence and Experience (1794) in the 1840s. The American interest in Blake's poetry is complemented by his fascination with the events in the Atlantic World in the years culminating in the American War of Independence. I will offer a reading of Blake's America: a Prophecy (1793) showing that the Civil War fulfilled his prophecy of inevitable future conflict. This is developed first by considering Ralph Waldo Emerson's changing responses to slavery and race during the turbulent middle decades of the century, and then by addressing Walt Whitman's attempt to negotiate postbellum America. This negotiation, I argue, results in the emergence of those two powerfully conflicting strains in his mature poetry: emancipatory fervour and simultaneous despair at the violence intrinsic in liberty.