Dred Scott was a slave who was owned by John Emerson, an army doctor from Missouri. Emerson traveled frequently as part of his job, and between 1834 and 1838 he took Scott with him to army posts throughout the United States and the western territories, including Illinois and the Minnesota Territory, where slavery had been outlawed by the Missouri Compromise. After Emerson's death in 1843, Scott sued in the Missouri courts for his freedom and that of his family, arguing that his stay in a free state and free territory had made him a free man.

The case was heard in the Supreme Court in 1856. It ruled against Dred Scott, dashing his hopes for freedom. When the Dred Scott ruling became public, Southern slave owners celebrated, confident that the issue had finally been laid to rest.

In the North, people were outraged. Many saw the decision as a call to arms; others who had tried to remain neutral on the subject of slavery found themselves compelled to join the abolitionist cause. The ruling also helped Abraham Lincoln become the first Republican president because it widened the divisions over slavery within the Democratic Party.