If Missouri was not admitted to the U. S. as a slave state, what would the South threaten to do?

The power shifted from Congress to the south.

Explanation:

If Missouri was not admitted to the U.S. as a slave state, the South threaten to prevent the admittance of Maine who applied for statehood in 1819 as a free state. Due to this admission of Missouri as a slave state the south agrees to allow admission of Maine as a free state with the Union. If this admission did not occur, the number of slave states are more than free states so due to admission of Missouri, the Maine was also admitted to the Union as a free state.

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