This is why I say the Dred Scott decision, in effect made slavery legal in every state, regardless that's state's laws on the subject.
It's a key point that nobody -- nobody -- understands.
In the late 1850s, the Slave Power was on the march, it was victorious, within a hair's breadth, within one more Supreme Court decision of having slavery declared constitutionally legal in every state.
Already in 1857 the Supreme Court said a slave-owner could take his slaves anywhere and maintain ownership.
So what was to prevent a slave-owner who brought slaves to, let's say, New York from selling his slaves to someone else while there?
And that is what had Northerners so outraged and enraged by the time of 1860s election.
What the Slave Power needed to do then was play it cool, give emotions time to settle down, and then work quietly to nail down their successes with further court decisions.
But unfortunately -- or fortunately depending on your point of view -- instead they took a path guaranteed to split the Union and start a Civil War.
The reason is the work of Southern Fire Eaters.
House Divided Speech
This point is made, not to be pressed immediately but, if acquiesced in for awhile, and apparently endorsed by the people at an election, then to sustain the logical conclusion that what Dred Scott’s master might lawfully do with Dred Scott in the free state of Illinois, every other master may lawfully do with any other one, or 1,000 slaves, in Illinois or in any other free state.
We cannot absolutely know that all these exact adaptations are the result of preconcert. But when we see a lot of framed timbers, different portions of which we know have been gotten out at different times and places and by different workmen — Stephen, Franklin, Roger, and James, for instance — and when we see these timbers joined together and see they exactly make the frame of a house or a mill, all the tenons and mortises exactly fitting, and all the lengths and proportions of the different pieces exactly adapted to their respective places, and not a piece too many or too few, not omitting even scaffolding, or, if a single piece be lacking, we see the place in the frame exactly fitted and prepared yet to bring such piece in — in such a case, we find it impossible not to believe that Stephen and Franklin and Roger and James all understood one another from the beginning, and all worked upon a common plan or draft drawn up before the first blow was struck.