Adams's defense of the prisoners from the Spanish slave ship Amistad goes down in history as a pioneering case in the fight against slavery.

It all started when Spanish slave traders kidnapped 53 Africans from Sierra Leone and took them to Cuba to be sold into slavery. On July 2, 1839, the prisoners rose up and took over the ship, killing some of its officers. When the Amistad entered American waters off Long Island, the Africans were taken ashore into custody by the U.S. Navy. President Martin Van Buren, eager for pro-slavery votes in the next election, wanted them returned to Cuba, but a Connecticut judge ruled that they had had a right to escape their captors by any means available.

The government appealed to the Supreme Court, where John Quincy Adams represented the 35 surviving prisoners. He won their freedom on March 9, 1841, and they returned to Sierra Leone in January 1842.