Haiti vs. the Dominican Republic
This is kind of ignoring the elephant in the room, which is that Haiti  was born from a successful slave revolt and and one of the first things it did as an independent country was to expel or kill virtually all the whites, expropriate their property and destroy all the institutions associated with them.  Both culturally and genetically (95.5% per Wikipedia), Haiti thus has a <i>lot</i> in common with sub-Saharan Africa, another notably poor part of the world, while the DR largely inherited the culture of their Spanish conquerors and rulers and genetics of both the Spanish and the indigenous inhabitants (well over half the country are mixed native&#x2F;white, only 15%-ish black).<p>Connecting the dots from this to their present sad state of affairs is obviously pretty controversial, but I need to note that aside from the obvious racist inferences, there are also many indirect paths.  For example, Haiti being both linguistically and culturally &quot;the odd one out&quot; in the neighborhood, they lack an obvious pool of culturally related investors to tap into, face racism from non-Haitians (relations between Haiti and DR in particular are <i>very</i> bad) and struggle to attract investment from the outside.