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:

answer; (a) he was a u.s senator for 38 years;