Answer :
Final answer:
One reason to support American expansion westward was the belief in Manifest Destiny.
Explanation:
One reason to support American expansion westward, according to Thomas Hart Benton, was the belief in Manifest Destiny. Manifest Destiny was the idea that it was the destiny of the United States to expand its territory from coast to coast. This belief fueled the desire for westward expansion and the acquisition of new land.
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