Institutions, not geography or culture, explain the wealth gap between nations

Acemoglu and Robinson's foundational claim is that neither geography (climate, disease burden, access to trade routes) nor culture (values, religion, work ethic) adequately explains why some nations grew rich while neighboring or similar nations stayed poor. Instead, they argue the decisive factor is institutions — the formal and informal rules determining who holds economic and political power and how securely that power is constrained by law.

They build this case through paired comparisons designed to hold geography and culture roughly constant while institutions differ sharply. The clearest example is Nogales, a single city split by the U.S.-Mexico border: essentially identical geography and largely shared cultural heritage on both sides, yet dramatically different income levels, life expectancy, and rule of law, tracking almost entirely with which country's institutions govern each half.

This institutional argument doesn't deny geography or culture matter at all, but it demotes them from primary causes to background conditions, with political choices about institutions doing the real explanatory work.

Takeaway: if two neighbors split by a border live in radically different worlds, the border itself — not the dirt beneath it — is the story.