What was the significance of the Dred Scot case?

In 1857, Dred Scott sued the United States government for
his freedom. He and his wife had lived as slaves in territories where slavery was
illegal. Scott had even lived outside the Missouri Territory (part of what was then new
western territories) where slavery was prohibited. Scott lost the case 7-2. The reason
was that no person of African ancestry, slave or free,
could claim citizenship and only a citizen could sue the
government.

The ruling effectively stated that slaves were
private property of their masters, so being on free soil did not affect their status as
slaves or free because private property trumps that. This called into question the
effectiveness of free territories, making emancipation for any slave seemingly
impossible. This invigorated the debate between abolitionists and pro-slavery
supporters. Slavery had been an issue for decades but the debate exploded in the 1850s
and you can see the proximity of the Dred Scott case (1857) to the start of the Civil
War (1861). This case was one of the events which arose from and contributed to the
slavery debate and the eventual war. This is particularly significant because it
addressed the issue of free soil and the expansion of slavery. Lincoln wanted, at least,
to halt the expansion of slavery. So, the issue was not just about North and South, but
the role of slavery in western expansion.

Dred Scott and
his wife were returned to former owners when their master's widow married an
abolitionist. They were freed in 1857, three months after their defeat at the Supreme
Court. Scott died in 1858 from tuberculosis.