On what ground did the Supreme Court rule against dred Scott

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Sandford, legal case in which the U.S. Supreme Court on March 6, 1857, ruled (7–2) that a slave (Dred Scott) who had resided in a free state and territory (where slavery was prohibited) was not thereby entitled to his freedom; that African Americans were not and could never be citizens of the United States

Dred Scott was the slave of an army physician who had lived in the Wisconsin Territory, where slavery was illegal. Upon returning to Missouri, Scott sued for his freedom on the grounds that he had once lived in a free territory. His case made its way to the U.S. Supreme Court.

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