One city, split by a fence, is the best argument in political economy
Same people, same climate, same food, and one side is three times richer. The reason isn't what you'd guess.
Nogales is a single city cut in half by the US-Mexico border. Nogales, Arizona and Nogales, Sonora share ancestry, cuisine, and the exact patch of desert. Average household income on the Arizona side runs about three times higher. Life expectancy is longer. Roads are paved. You can vote out a mayor who fails you.
Daron Acemoglu and James Robinson use this split city to open Why Nations Fail, and the argument that follows is deliberately unglamorous: it isn't geography, culture, or the legacy of colonization by itself that explains why nations end up rich or poor. It's whether their institutions are inclusive, protecting property, allowing broad participation, letting failure and success both have consequences, or extractive, built mainly to funnel wealth upward to whoever already holds power. Nogales, Sonora spent most of the twentieth century under one party's near-uninterrupted control. Nogales, Arizona did not.
The uncomfortable implication is that most "development" advice, build infrastructure, attract investment, train workers, treats a symptom. The disease is who gets to keep what they build.