For decades historians believed Genghis Khan’s drive to build the largest contiguous land empire in history was based, in part, on a desire to break out of Mongolia’s unpredictable, drought-plagued realm into more fertile areas. Amy Hessl, a geography professor from Eberly College in West Virginia, is turning that theory on its head. And it’s all because of tree rings.
In 2010, when Hessl was in Mongolia, “We walked way out on a lava flow and found some old wood that nobody had collected,” she told National Geographic Radio. The oldest dated back to 658 CE. Further study revealed that, “In the early 1200s, when Genghis Khan came to power, the rings were consistently large for several decades—a period of wet conditions that was unprecedented in almost 2,000 years.” If her analysis is validated with more research, it means Genghis and his horde had the luxury of using Mongolia’s rich grasslands to amass huge numbers of horses for their army and supply trains. Then they rode out of the steppes to conquer the world.