Final answer:
Ralph Waldo Emerson is the author who described poetry as a 'meter-making argument' and whose transcendentalist movement impacted American literature significantly.
Step-by-step explanation:
The author who defined poetry as a 'meter-making argument' and stands as a pivotal figure in American literature is Ralph Waldo Emerson. Emerson was an American essayist, lecturer, and poet, who led the transcendentalist movement of the mid-nineteenth century. This movement emphasized philosophical principles that went beyond the physical and empirical and was forefront of shaping the individualist and naturalist ideals in American literature.
While Emily Dickinson and Walt Whitman are also critical figures in American literary history, Emerson's work and philosophy shaped their progress and contributions. Dickinson's poetry often defied conventional form and content, reflecting her private life and introspective nature. Whitman, on the other hand, is well-known for his work 'Song of Myself', which presented a new form of poetry that celebrated the individual and the collective spirit of America. These authors embraced the spirit of Romanticism, seeking originality and freedom of self-expression, which was an extension of the ideals Emerson championed.