Final answer:
The US victories at the Battle of Thames and the Battle of Horseshoe Bend weakened British support for their Native American allies and significantly impacted the War of 1812 by allowing American control over the Great Lakes and facilitating westward expansion.
Step-by-step explanation:
The primary effect of the US victories at the Battle of Thames and the Battle of Horseshoe Bend was b. Weakened British support for Native American allies. The US victories at the Battle of Thames and the Battle of Horseshoe Bend weakened British support for their Native American allies and significantly impacted the War of 1812 by allowing American control over the Great Lakes and facilitating westward expansion.
These battles marked significant turning points during the War of 1812. The death of Tecumseh at the Battle of Thames dealt a heavy blow to the Native American confederation he led and diminished the resistance against American forces. Without the strategic partnership with the Native Americans, British influence and control in the region waned. The Americans were able to regain control over the Great Lakes, which helped to shift the focus of the war southward and accelerated westward expansion, thereby undermining Native American and British efforts to halt American growth.