The short answer is: "to a great extent". The entire plan of the Federalists was to create a strong central government instead of having many autonomous states. Of course this occasionally went against national unity in the sense that some people were opposed to this plan, but in general they favored unity.
This is a personification. An idiom would be something like a proverb while hyperbole would be exaggeration. A metaphor is when there's a meaning that's implied. Personification is when you give objects that don't behave like people, human traits. The raven in reality probably doesn't say anything, just croaks or whatever, but in the poem he keeps saying it because it's a poem.
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Answer:
Checks and Balances help make sure no branch is more powerfl than the others.
Explanation: