The voyage of the Amistad began on June 28, 1839 in Havana, Cuba (which belonged to Spain), where the 53 Africans had purportedly been bought as slaves. The ship was headed to Puerto Principe, Cuba. However, on July 2, 1839, the African Cinqué was able to free himself and the other captives. They killed the ship's cook (who had earlier scared the slaves by describing how they would be killed and eaten upon arrival) and the captain in a struggle in which two of the Africans also died. Two sailors escaped. The lives of the two purported slaveowners, Ruiz and Montez, were spared, with the understanding that they would steer the ship to Africa. The captain's personal slave also survived.
The navigator managed to deceive the Africans and steered the Amistad north along the coast of the United States, where the strange ship was sighted repeatedly. They arrived off Long Island, New York on August 26, 1839, and anchored within half a mile of the shore. Some of the Africans went on shore to procure supplies of water and provisions, and the vessel was then discovered by the United States naval brig Washington. Lieutenant Gedney, commanding the Washington, assisted by his officers and crew, took possession of the Amistad, and of the Africans on shore and in the vessel, brought them into the District of Connecticut, and there presented a written claim under admiralty law (that is, a libel) for salvage of the vessel, the cargo, and the negroes. It has been alleged that Gedney chose to land in Connecticut, because, unlike in New York, slavery was still technically legal there (though extremely rare), and he hoped to profit from the slaves.
A case before the United States Circuit Court in Hartford was filed, alleging mutiny and murder. Various parties also claimed property rights to the slaves: Ruiz and Montez, Lieutenant Gedney and Captain Henry Green (who had met the Africans while on shore in Long Island and claimed to have helped in their capture). The Spanish government asked that the ship, cargo and slaves be restored to Spain under the Pinckney treaty of 1795 between Spain and the United States. Article 9 of this treaty holds that "all ships and merchandises of what nature soever, which shall be rescued out of the hands of pirates or robbers on the high seas, [...] shall be restored, entire, to the true proprietor." The judge ruled that the court lacked jurisdiction as to the mutiny and murder charges, because the alleged acts took place on a Spanish ship in Spanish waters. He directed the U.S. District Court to sort out the various property claims.
The abolitionist movement had formed the "Amistad Committee" and collected money to mount a defense of the Africans. Their main argument before the District Court was that a treaty between Britain and Spain of 1817 and a subsequent pronouncement by the Spanish government had outlawed the slave trade across the Atlantic. It was established that the slaves had been captured in Mendiland (current Sierra Leone) in Africa, sold to a Portuguese trader in Lomboko (south of Freetown) in April 1839, and brought to Havana illegally on a Portuguese ship. The Africans were therefore not slaves, but victims of illegal kidnapping and free to go. Their papers wrongly identified them as slaves that had been in Cuba since before 1820, a common practice in Cuba condoned by government officials.
Initially, communication with the Africans was difficult, since they didn't speak English or Spanish. Professor Gibbs learned to count to ten in their native Mendi language, went to the harbor of New York City, and counted out loud until he located a person able to understand and translate.
The abolitionists filed charges of assault, kidnapping, and false imprisonment against Ruiz and Montez. Their arrest in New York City in October 1839 outraged conservatives and the Spanish government. They were eventually released on bail and left for Cuba.
U.S. President Martin Van Buren, who did not have strong opinions on the slavery question but was concerned about relations with Spain and about his reelection prospects in the southern states, sided with the Spanish position; he ordered a U.S. schooner to the New Haven harbor to return the Africans to Cuba immediately after a favorable decision, before any appeals could be decided.
The District Court however agreed with the abolitionists, ordered that the Amistad be given to Spain and the Africans be returned to their homeland by the U.S. government. (The federal government had outlawed the slave trade between the U.S. and other countries in 1808, and a law from 1818, amended in 1819, provided for the return of all illegally traded slaves.) The captain's slave was declared the rightful property of the captain's heirs and was ordered restored to Cuba (he escaped to Canada).
The U.S. district attorney, on order of Van Buren, immediately appealed to the Circuit Court. This court upheld the decision in April 1840 but nevertheless forwarded the case to the U.S. Supreme Court for a final decision because of its international importance.
John Quincy Adams, congressman from Massachusetts and former President of the United States, agreed to argue the case before the high court. The Supreme Court ruled that the Africans had never been the legal property of Ruiz and Montez, that (therefore) article 9 of the Pinckney treaty did not apply to them, and that they were free. The US law from 1818 did not apply to them either since they had not been brought to the US in order to be sold, and the federal government was thus not obliged to pay for their return to Africa. The one dissenting judge also essentially agreed with these findings.
Ironically Cinqué, once returned to Africa, set himself up as a slave trader.
The Amistad committee continued to instruct the Africans in English and Christianity and collected donations to pay for their return. Along with several missionaries, the surviving 36 Africans travelled back to Africa early in 1842, and a mission was erected in Mendiland. The Amistad committee later evolved into the American Missionary Association, an evangelical organization which continued to support the Mendi mission, argued for abolitionism, and eventually established many schools for freed slaves in the U.S.
In the following years, the Spanish government continued to press for compensation, and several lawmakers from southern states introduced resolutions into Congress to pay. These efforts were supported by presidents James K. Polk and James Buchanan, but they all failed.
A simplified version of the events described here was made into a movie called Amistad in 1997. It was directed by Steven Spielberg and starred Anthony Hopkins as John Quincy Adams, Djimon Hounsou as the African's leader Cinqué and Matthew McConaughey as their lawyer. This film described some of the terrible things that allegedly happened to some of the slaves in the ship, such as group drownings (by tying a number of slaves with one rope and making them fall to the sea) and death by hunger.