Final answer:
The provided information does not include details about the poem that earned John Greenleaf Whittier national fame, but rather it discusses the poet Walt Whitman and his famous work 'Leaves of Grass' and 'Song of Myself.'
Step-by-step explanation:
The poem that earned John Greenleaf Whittier national fame was not mentioned in the provided text. Instead, the text focuses on the poet Walt Whitman, a 19th-century American poet known for his work Leaves of Grass and the poem "Song of Myself." Whitman's poetry, which delves into the transcendentalist movement and celebrates individualism and the common man, garnered attention and was groundbreaking at the time of its publication. Whitman's style, free of traditional rhyme and meter, presented a novel form that reflected the changing nation.
The provided information does not specify the work that brought Whittier fame; instead, it highlights Whitman's achievements and describes his impact on American literature through his poems, particularly in his portrayal of the transcendentalist ethos and his use of the common language of the people.