Some disasters hurt society (Hurricane Katrina in 2005). Bigger ones permanently alter it (the Black Death in the 1300s; Mao's Great Leap Forward). The worst of disasters completely destroy a civilization and leave behind so few they take centuries to recover (the Mongolian slaughter of Iran in the 1200s; the smallpox epidemic among Native Americans). 

Today we look at the tipping points between a society being hurt and a society being mortally wounded.

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