Final answer:
Isaac Watts is recognized as America's most beloved hymn writer of the nineteenth century, whose hymns significantly influenced the hymn singing tradition in the country, especially among African American communities. His works were popularized further through the publication 'Slave Songs of the United States', edited by William Francis Allen.
Step-by-step explanation:
The most beloved hymn writer of the nineteenth century in America was Isaac Watts. He was largely influential in shaping the tradition of hymn singing in America as his hymns were spread by Baptist, Methodist, and Presbyterian missionaries during the eighteenth and nineteenth century, including into African American slave communities. Notably, his hymns were 'lined-out'—a technique that later influence the distinctive musical style of African American communities. Watt's hymns were further popularized by William Francis Allen, a northern educator, who heard the religious singing of newly freed slaves during the Civil War, and edited and published the first collection of African American religious songs in American history, titled 'Slave Songs of the United States'.
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