Southern states opposed the Compromise of 1850 because

As a South Carolina senator, Calhoun used the argument of states' rights to protect slavery in what is known as the Nullification Crisis of 1832-1833. At the end of his senatorial career, Calhoun opposed the Compromise of 1850 because of its proposed limits on slavery during the westward expansion of the nation.

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Explanation:

president thomas jefferson commissioned the expedition shortly after the louisiana purchase in 1803 to explore and to map the newly acquired territory, to find a practical route across the western half of the continent, and to establish an american presence in this territory before britain and other european powers