At the start of the 1789 French Revolution, the Island of St. Dominigue, nowadays known as Haiti, was France's biggest and most prosperous colony, employing 1000 ships and 15,000 French sailors.
However, this island was, like many other lands in the 18th century, run by slaves, primarily from Africa. These slaves didn't like being slaves (obviously), and a significant step in their freedom was the Declaration on the Rights of Man in 1789, that became a part of the new French Constitution. It stated that “In the eyes of the law, all men are equal”, which seemed to mean that the slaves should be freed. The new government didn't want to release this to their colonies, but word leaked out.
In 1790, an outbreak of revolution led by Vincent Ogé swept the countryside. This revolt was caused by a ruling from the National Assembly that didn't let mulattoes (people of mixed descent) vote. This was the first thing that caused the Haitian Revolution.
In 1791, a full-scale revolution broke out, and former slaves were burning plantations and killing their owners. French Republican forces joined them to free the island from the oppression of the old government. The British joined in the fray to try to take the island, working on the revolutionaries' side.
The leader of the revolutionaries, a black named Toussaint started making his own independent country, but he was captured and taken to France, where he died in prison. However, the revolutionaries managed to make Haiti an independent nation after their leader's death.