999's link is indeed a good start.    It's certainly true that the French considered the island their crown jewel.   Sugar plantations made colonial operations fabulously wealthy--and not just on Hispaniola.   As I recall it was a burning issue right after the 7 Years War as to whether Hispaniola or Canada was more valuable.

It's also true, as the Haitian Ambassador pointed out, that there's a link between Haiti and the Louisiana Purchase: after the successful Sainte Domingue revolt, Napoleon decided it was better to get some money for European operations and sell off French holdings in the Western Hemisphere--probably also did not mind strengthening a rival to Great Britain.

But any explanation of Haiti's poverty which leaves out misgovernment is misleading.