Small shocks become large at the margins, and compression carries them far. A swing of one or two degrees changed little in the south of Europe, but "at the extreme edges of human habitation, even such slight degree changes had outsized effects. People living on the edge went over the edge." The climate "worked Scandinavia like a bellows," Russia then "compressed the Central Asian grasslands, setting off ripple effects that were felt across thousands of miles." A system's most exposed members are where a perturbation is amplified and launched; that the same holds for communities and markets near a threshold is Clay's extension, not Ansary's.

Evidence 3 passages

• groundsSource document

  These fluctuations weren't enough to make much noticeable difference in the South, but in the far north, at the extreme edges of human habitation, even such slight degree changes had outsized effects. People living on the edge went over the edge.

• backsSource document

  From the 8th to the 11th centuries, the environment worked Scandinavia like a bellows. It let the population grow, then clamped down and blew out boatloads of predatory warriors with nothing to lose.

• backsSource document

  The rise of Russia compressed the Central Asian grasslands, setting off ripple effects that were felt across thousands of miles of territory.

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