On March 6, 1857, a divided Supreme Court announced its landmark Dred Scott decision. A narrow majority held that slave or free, blacks were not American citizens and therefore could not sue in American courts. Furthermore, Chief Justice Roger B. Taney, himself a former slaveholder, announced that Congress had no lawful power to prohibit slavery in federal territories.

The Know-Nothings evolved out of a secret nativist organization, the Order of the Star-Spangled Banner, founded in 1850. (The party's popular name, Know-Nothing, derived from the standard response of its members to inquiries about its activities: "I know nothing.") This order was one of many such societies that mushroomed in response to the unprecedented immigration of the 1840s.

In 1854, a major filibustering enterprise overlapped the official efforts to buy Cuba. The leader of this venture was former Governor John A. Quitman of Mississippi…During the 1850s, American filibusters, mostly from Texas and California, launched dozens of raids into Mexico. Some of them had simple plunder as their goal; others were part of a sporadic border warfare that continued for years after the Mexican war.

In March 1857, the U.S. Supreme Court upheld the legality of slavery in the case of a slave named Dred Scott. Scott claimed his freedom because his owner had moved him from a slave state (Missouri) to a free state (Illinois). U.S. Chief Justice Roger Taney held that a slave, ex-slave, or descendant of a slave was not an American citizen, but the property of an owner. Because Congress was constitutionally required to protect property, it could not prohibit slavery in the territories.

Northern moderates accepted the Fugitive Slave Act as the price of saving the Union. But the law contained a string of features distasteful to moderates and outrageous to staunchly antislavery northerners. It denied alleged fugitives the right of trial by jury, did not allow them to testify in their own behalf, permitted their return to slavery merely on the testimony of the claimant, and enabled court-appointed commissioners to collect ten dollars if they ruled for the slaveholder but only five dollars if they ruled for the fugitive.