*Adams had resisted, but finally accepted, similar entreaties two years earlier to join the defense team on behalf of a group of Africans who had revolted aboard the Spanish slave ship Amistad, killing the captain and another member of the crew. Like Britain and the United States, Spain had outlawed participation in the Atlantic slave trade, but Spanish slave dealers flouted the ban, seizing Africans for shipment to the Spanish colony of Cuba, where they were provided with false papers claiming they were Cuban-born. The Amistad had been transporting a group of some fifty such slaves along the Cuban coast from Havana to buyers who had purchased them with the intent of putting them to work in the sugar fields. After taking over the ship, the slaves tried to compel the Spanish crew to sail them back to Africa, but by turning by night toward the northwest, the Spaniards managed to steer the Amistad into Long Island Sound, where a U.S. Coast Guard cutter seized the vessel. The Africans were imprisoned in New Haven, Connecticut, pending resolution of their fate by U.S. courts.

Spain demanded return of the slaves and the U.S. government agreed, but antislavery attorneys, led by Roger Baldwin of Connecticut, intervened. After lower courts ordered the Africans released on the grounds that Spain had violated the ban on the international slave trade, the U.S. government appealed to the Supreme Court, and Adams joined the defense. In the winter of 1841, for more than eight hours over more than two days, he argued on grounds of natural law that the case against the slaves was a travesty of justice. The high court sustained the lower courts, and the slaves were released, but although Justice Story called Adams’s performance “extraordinary,” the ruling was a narrow one, confirming the claim by the defense that identification papers issued to the slaves were false and that they had been kidnapped, transported, and sold in violation of an international agreement banning the slave trade. In other words, they had never been legally slaves. (For a brief and clear account of the case, see William J. Cooper, The Lost Founding Father: John Quincy Adams and the Transformation of American Politics [New York: Liveright, 2017], 362–68.)