Final answer:
The word "backbreaking" in the context of the Transcontinental Railroad's construction adds a somber and respectful tone to the narrative by highlighting the immense physical hardship and strenuous labor endured by the workers.
Step-by-step explanation:
The word "backbreaking" significantly affects the tone of the sentence by emphasizing the extreme physical hardship and strenuous labor endured by those who constructed the Transcontinental Railroad. The term conveys a sense of the grueling and physically demanding work that the laborers, often immigrants and veterans, had to endure. It highlights not just the physical strain but also the arduous and punishing conditions under which the workers toiled, painting a somber and respectful tone towards their effort.
The use of this adjective suggests that the construction of the railroad was no easy feat but rather an accomplishment achieved through immense sacrifice and resilience. By choosing a word with such a strong connotation, the author adds a layer of gravity and solemnity to the historical narrative, acknowledging the human cost of such a monumental engineering project.