Final answer:
Relations with Native Americans influenced the decision of Congress to declare war on Britain, as Britain's support of Native resistance threatened American territorial expansion and sovereignty.
Step-by-step explanation:
Native American relations significantly influenced Congress's decision to declare war on Great Britain due to the British support of Native American resistance against American expansionist desires. The British endorsement of the Proclamation Line of 1763, which restricted American settlement beyond the Appalachians, was seen as a protective measure for Native lands, tipping many tribes towards supporting the British during the American Revolutionary War. However, the War of 1812, sometimes called America's "Second War of Independence," saw the British again leveraging tribal discontent, impressing American sailors and supplying Native tribes with arms, contributing to Congress's decision to declare war due to the perceived threat to American sovereignty and expansion. However, some native peoples did side with the Americans, particularly in New England where they had closer relationships with colonial neighbors.