By common consensus, Dred Scott v. Sanford is the most infamous decision in Supreme Court history.

Ironically, it also may be the most significant decision in Supreme Court history.

Why? Because it almost destroyed the Union.

Here's what happened. In 1846, Dred Scott, a slave, sued for his freedom.

Scott had been born into slavery in Virginia, but during the 1830s, he traveled with his owner,

John Emerson, an army doctor, to Illinois and the Wisconsin Territory, both of which had banned slavery.

When Emerson died in 1843, his widow, Irene Sanford, inherited Scott.

In 1846, Scott sought to buy his freedom from Sanford, offering her $300.

She refused.

Scott then turned to the legal system filing a lawsuit against her

in a St. Louis Missouri court. He had a strong case. It was not uncommon for slaves to claim that once

they entered a free state, they were free, and Missouri courts were sympathetic to these claims.

Over the next eight years, however,

Scott endured a legal rollercoaster, first losing his case, then winning, then losing again.

His appeal reached the Supreme Court in February 1856. Chief Justice Roger Tani immediately grasped

its importance. Here was a case, Tani reasoned, that could

settle once and for all the vexing issue of slavery and its role in America's future. To understand

Tani's thinking, we need a bit of historical context. As the nation expanded in the early and

mid-19th century and admitted new states,

the slavery issue became more and more contentious.

In 1820 and then again in 1850, Congress passed two bills to diffuse the growing conflict,

respectively known as the Missouri Compromise and the Compromise of 1850. Both laws divided the country

...