Climate change may have helped the infamous Genghis Khan expand his empire.

Researchers looked at tree rings in Mongolia to determine how the climate has changed throughout history and how these changes interfered with the takeover of the Mongol Empire across northeastern Asia, a National Science Foundation news release reported.

The tree rings revealed there had been many changes in water availability in the region. The timing of these precipitation fluctuations suggest that Genghis Khan gained power during the time of a drought. On the other hand the times when his empire spread most successfully across the region tended to be the wettest.

"Through a careful analysis of tree-ring records spanning eleven centuries, the researchers have provided valuable information about a period of great significance," Tom Baerwald, a program director for the National Science Foundation's (NSF) Dynamics of Coupled Natural and Human Systems (CNH) Program, which funded the research, said in the news release.

"The results also provide insights into the complex interactions of climate, vegetation and human activity in semi-arid regions today," he said.

Rainier conditions would have provided more grass for the army horses to graze on, allowing for a boost in literal "horse power."

"Such a strong and unified center would have required a concentration of resources that only higher productivity could have sustained, in a land in which extensive pastoral production does not normally provide surplus resources," the paper said, the news release reported.

Mongolia is currently in drought conditions, most likely as a result of man-made global warming.  

"If future warming overwhelms increased precipitation, episodic 'heat droughts' and their social, economic and political consequences will likely become more common in Mongolia and Inner Asia," the paper said, the news release reported.

The conditions in Mongolia today are very similar to the climate when Genghis Khan first came to power.