The question of whether slavery would be permitted in new territories had threatened the Union beginning in the 1780s. This question was raised in 1857 before the Supreme Court case of Dred Scott v. Sanford.  Dred Scott was a slave of John Emerson, and had been taken from Missouri to posts in Illinois and what is now Minnesota for several years in the 1830s, before returning to Missouri. The Missouri compromise of 1820 had declared the area including Minnesota free.

In 1846, Scott sued for his freedom on the grounds that he had lived in a free state and a free territory for a prolonged period of time. Finally, after 11 years, his case reached the Supreme Court.

• The court ruled that Scott’s “sojourn” of two years to Illinois and the Northwest Territory did not make him free once he returned to Missouri. Slave states did not have to honor the “once free, always free” rule.
• The court further ruled that as an African American man, Scott was excluded from United States citizenship and had no rights in federal court.
• The court ruled that the congress never had the right to prohibit slavery in any territory. Any ban on slavery was a violation of the Fifth Amendment. The Missouri compromise was therefore unconstitutional.

Source: The Dred Scott Decision
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