The Amistad rebellion and the court case that followed also came at a critical time in the history of slavery and abolition. The early 1830's marked the beginning of William Lloyd Garrison's crusade against slavery, and more northern churches began to take it up as a moral crusade, as did women reformers of the time.
The case also represented a constitutional milestone, in that it was the first major case ruling on the legal status of blacks/slaves. While the Amistad slaves were freed eventually, it is important to note that the ruling was based more on property laws/rights than it was on human rights. In fact, the Supreme Court was even more conservative on the subject later on in the 1850's with the Dred Scott decision.
The incident you are referring to occurred when slaves being brought from one part of Cuba to another aboard the ship Amistad rebelled and took over the ship. This happened in 1839.
After the slaves took over the ship, they tried to force the navigator to bring them back to Africa. He tricked them and sailed north. They ended up being found by the US Navy off of New York. The slaves were taken to Connecticut to be resold.
When abolitionists heard about this, they started to protest and the case was taken to the US Supreme Court. The Court ruled that the slaves could not be sold and they were set free.
Although it did nothing to help end slavery, this rebellion is seen as having been very important in helping energize the cause of abolitionism in the US.
The rebellion resulted in the release of the slaves and sparked the cause for abolitionism in the US.
The Amistad was a Spanish slave ship that dramatically seized off the coast of Cuba by the enslaved Africans aboard. The ship was driven ashore in Long Island and they were put on trial. John Quincy Adams argued their case before the Supreme Court, securing their eventual release.