The Presidential Daily Brief


  1. Tree Rings Suggest Uncommon Climate Helped Genghis Khan

    In 1211, Genghis Khan ruled over Mongolia. By 1225, his empire stretched from coastal China to the Caspian Sea. It seemed improbable that nomads dominated the continent so quickly, but researchers now believe they know how it happened: with lots of rain. Core samples of millennium-old Siberian pines in Asia show that during the empire’s rise, the region experienced 15 unprecedented years of sustained wet, warm weather. The rain meant more grass, healthier horses and stronger invaders — which probably left the conquered singing “rain, rain, go away.”

    Sources: CS MonitorLA TimesNational Geographic

This story is part of The Presidential Daily Brief

view full edition