Why was missouri's admission to american statehood in 1819 controversial?

Missouri’s admission to American statehood in 1819 was controversial because it raised question on whether slavery should be expanded westwards. Henry Clay proposed that slaveholders be prohibited from bringing new slaves to Missouri. The dispute was resolved through the Missouri Compromise that paired the admission of slave and free states

the monroe doctrine is the best known u.s. policy toward the western hemisphere. buried in a routine annual message delivered to congress by president james monroe in december 1823, the doctrine warns european nations that the united states would not tolerate further colonization or puppet monarchs.

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