The rare moment when a system's path forks, plague, revolution, invasion, and the small difference at the fork becomes the permanent difference after it.
Documented
The plague experiment
Acemoglu and Robinson's showcase: the Black Death (1347-51) hit Eastern and Western Europe equally, but in the West it broke the labor system, peasants bargained wages up, while in the East landlords responded with the second serfdom, binding peasants harder. Same shock, opposite institutions, divergence locked in for centuries.
Assessment: Documented: the divergence is standard economic history; the mechanism attribution is the book's.
Stories
The butterfly budget
The popular version: history turns on accidents, so anyone's moment could be the hinge. Comforting and half-true, junctures multiply possibilities but institutions decide which possibilities survive the decade.
Assessment: Stories: the contingency is real; the 'anyone' part is the fairy tale.
Interesting claims
The hinge that keeps swinging
The uncomfortable extension: if junctures set paths, we may be inside one now, platforms, algorithms, and incentives calcifying into the century's institutions while we call them apps. The book's readers overwhelmingly assume they live in the inclusive aftermath; the framework does not promise that.
Assessment: Interesting: the authors have said as much in later work; the optimism is the readers' import.
Sources and further reading
Acemoglu and Robinson, Why Nations Fail (2012), Black Death divergence analysis
David Landes vs. institutionalist debates on the second serfdom
Collier and Collier, Shaping the Political Arena (1991), the framework's origin
Worth asking
Is history a river with a direction, or a pinball table with memory?