Final answer:
American Romantics were concerned that westward expansion would tear the United States apart, threatening its unity and harmony.
Step-by-step explanation:
The concept of 'manifest destiny' was a concern for American Romantics because they believed that westward expansion would tear the United States into pieces. They feared that expanding the nation's territory would lead to internal divisions and conflicts, weakening the unity and harmony of the country. This concern was rooted in the belief that the United States was a unique and special nation that needed to stay united in order to fulfill its destiny.
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