Hello again, Genie. I thought you might find this interesting.
Also see Who Really Wrote "I Heard the Bells on Christmas Day" from Harvard Magazine, 1991. The article says that although Longfellow wrote the poem, an unknown person dropped verses and added a last verse, and put the tune to music in 1872. -Joe Offer-

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I Heard the Bells on Christmas Day

        In spite of the mentions of bells and Christmas in the title, "I Heard the Bells on Christmas Day" is as much an antiwar song as it is a pro-Christmas song. The poetry of this renowned carol was crafted by the great American literary figure, Henry Wadsworth Longfellow (1807-1882), in the midst of the American Civil War. On Christmas Day in 1863, Longfellow wrote the familiar lines in response to the horror of the bloody fratricidal conflict in general and to the personal tragedy of his son, Lieutenant Charles Appleton Longfellow, who was severely wounded in November 1862.
        This was not the only pacifist poetry composed by Longfellow. His peace sentiments found their way into many poems, including the famous "Song of Hiawatha" (1855) and "Courtship of Miles Standish" (1858). Although his reputation rests primarily on his considerable skill as a popular poet, which also resulted in the well-known works "The Village Blacksmith," (1841), "The Wreck of the Hesperus" (1841), "Evangeline" (1847), and "Paul Revere's Ride" (1863), his deep-rooted pacifism, as well as his concern with social issues such as slavery, should not be overlooked in the understanding of the man.
        It was not until sometime after 1872 that the 1863 poem, which was originally titled "Christmas Bells," was converted into a carol. Some unknown person in some unknown year recognized that Longfellow's stirring and optimistic interpretation of the bells of Christmas would make a magnificent mate for an 1872 processional which was strongly reminiscent of the ringing of bells. The composer of the appropriate tune, John Baptiste Calkin (1827-1905), was the most famous of a family of accomplished English musicians. At first Calkin `s melody was published with the 1848 American hymn, "Fling Out the Banner! Let It Float" by George Washington Doane (1799-1859). Ironically, "Fling Out" was an old-fashioned militant missionary hymn which contrasted greatly in purpose and spirit from the more permanent partner of Calkin's music, "I Heard the Bells."
        Although Calkin's melody is a beautiful, gentle, and lofty rendition of the sounds of Christmas bells and is quite well received during the holidays, at least three alternative tunes have been tried. These are the moderately popular wafting melody by Johnny Marks (1909-1985), who is most noted for "Rudolph the Red-Nosed Reindeer," plus tunes by John Bishop (ca. 1665-1737) and Alfred Herbert Brewer (1865-1928). Calkin's melody, however, remains predominant over the others.
        As a pair, the resonant tones of Calkin's pensive music, the main component of his reputation, and the minor but excellent poem by Longfellow, comprise a very satisfying carol. On top of its fine artistry, it offers an undeniable moral whose essence resides in the two phrases with which each stanza ends. "Peace on earth, goodwill to men" so appropriately covers both halves of the partly Christmas and partly pacifist carol. No matter how long this particular song may endure, may its two highly desirable themes harmoniously blend together in an everlasting symbiosis for the benefit of humanity.

from The Christmas Carol Reader, William Studwell, 1995.