B because we weren't imperialized during the war.
Answer:
The First Battle of Bull Run, also known as the Battle of Manassas, marked the first major land battle of the American Civil War. The Confederate victory gave the South a surge of confidence and shocked many in the North, who realized the war would not be won as easily as they had hoped.
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The American attitude shifted in favor of rights for Native Americans. This is based on "Polls showed that Americans believed in rights for Native Americans". Why it's not B is because it wasn't the polling that contributed to the act, but what the polls showed which is C.
A: Slavery Might Become Legal Everywhere
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