Based on historical perspective, the period of expansion between 1842 and 1853 was so significant to the development of the United States because "it made the country fulfill its Manifest Destiny and balance the issue of slavery."
Manifest Destiny is the term for the belief among the Americans in the 19th century that God has made it for them to expand their sovereignty and spread democracy and capitalism over the continent it belongs.
Hence, in this case, it is concluded that the period of expansion between 1842 and 1853 was so significant to the development of the United States.
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