Which idea provided justification for the westward expansion of the united states during the first half of the 19th century?.

Manifest Destiny

Manifest Destiny, a phrase coined in 1845, is the idea that the United States is destined—by God, its advocates believed to expand its dominion and spread democracy and capitalism across the entire North American continent.

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Explanation:

both include an amendment process.

a.

congress passed laws allowing for free passage between states.