Many have argued that American Unitarianism originated solely from within Congregationalism and developed independent of outside influences. William Ellery Channing's "Unitarian Christianity" sermon in 1819 was a key moment in the history of the denomination, as Channing consciously sought to define the parameters of the faith and eliminate all vestiges of competing influences. Yet the American Unitarian tradition was far more complex than its nineteenth-century adherents were willing to admit. In Joseph Priestley and English Unitarianism in America, J. D. Bowers reexamines its...