There were several such territories, like Maine and California.
Please be more specific.
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Free state.
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Congress maintained that it was treasonable for a state to
secede from the USA.
The South maintained that the USA had started as a voluntary
union of states, and that any state was free to quit.
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No. The Dred Scott decision basically said all the states of the
USA were slave states and a slave in a "free" state was still a
slave. The Dred Scott decision helped to lead to the Civil War.