Final answer:
The United States declared war in 1812 to defend the frontier from Native American uprisings.
Step-by-step explanation:
One of the reasons for the United States declaring war in 1812 was to defend the frontier from Native American uprisings. The British had been supporting Native American resistance against American expansion into the western territories, which threatened the Native American tribes' lands and resources. The United States saw this as a threat to its sovereignty and declared war.
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