The crisis—in which thousands of Dominicans of Haitian descent have been stripped of their citizenship and “repatriated” to Haiti—exposes the photo-negative relationship between the two countries sharing Hispaniola, an island about the size of West Virginia. In 1960, the Dominican Republic and Haiti were utterly comparable: two plantation societies, both former European colonies. Real per capita GDP was the same in both, at just below $800 annually. Both countries suffered under brutal strongmen. In Haiti, development was neglected by the Duvaliers, the father-son dynasty that ruled from 1957 to 1986. Across the border, the Trujillo and Balaguer regimes, which ruled on and off from 1930 to 1994, promoted Dominican agriculture, industry, and public works (while otherwise consolidating a crony plutocracy). By 2005, the Dominican Republic’s GDP had more than tripled. Haiti’s had halved. The Dominican Republic is now considered a middle-income country, and Haiti is the poorest country in the Western Hemisphere.

The contrast is visible from many points along the 234-mile border dividing Hispaniola. To the east, lush green forest cover is irrigated for the Dominican Republic’s banana farmers. To the west it’s almost sepia-toned: Vast tracts of land have been cleared for charcoal, Haiti’s primary cooking fuel, resulting in arid soil and sediment-loaded rivers.

Antihaitianismo is as old as the Dominican Republic, which won independence from Haiti in 1844. (After Haitians expelled the French and established their own country in 1804, they invaded and conquered the eastern part of the island, then a Spanish colony, in 1822.) Haitian immigration to the Dominican Republic took off during the early 20th century. Faced with drought, Haitian peasants would cross the border to work the zafra, or sugar-cane harvest; many stayed and put down roots. During the Trujillo regime, antihaitianismo was public policy. In 1937, on direct orders from Trujillo, the Dominican military committed an act of genocide, ordering laborers in the borderlands to say the word for “parsley” and executing those whose pronunciation betrayed their Haitian origins. As many as 20,000 people were killed in what became known as the Parsley Massacre. Still, overpopulation, poor infrastructure, and the lack of wage labor continued to drive the most desperate Haitians across the border into the Dominican Republic.

And it’s back across this border that many have crossed, since some 200,000 Dominicans of Haitian descent were stripped of their citizenship in 2013. For most of its history the Dominican Republic offered birthright citizenship, except to those born “in transit,” such as the children of diplomats and tourists. In September 2013 the Constitutional Tribunal, the Dominican Republic’s highest court, expanded that caveat to retroactively include everyone born to undocumented immigrants since 1929. “Nationality ... is not only a legal bond,” the court argued in its ruling, but involves among other things “a set of historical, linguistic, racial and geopolitical traits.” Those who do not share these traits, it implied, do not share Dominicans’ “particular idiosyncrasies and collective aspirations.”