Might unusually warm weather in the 13th century given the Mongols what they needed to conquer much of the known world?

Beginning in the 13th century, the Mongol Empire spread across Asia and into the Middle East like wildfire, growing into the largest contiguous land empire the world has ever seen.

Historians have long speculated that periods of drought pushed the Mongol hordes to conquer their neighbors, but preliminary new findings suggest that theory may be exactly backward. Instead, consistent rain and warm temperatures may have given the Mongols the energy source they needed to conquer Eurasia: grass for their horses.

This idea, bolstered by the discovery of tree rings that preserve a climate history of Mongolia back to 657 A.D., is still in the preliminary stages of investigation. LiveScience spoke with Amy Hessl, the dendochronologist, or tree-ring researcher, who along with collaborators Neil Pederson and Baatarbileg Nachin first discovered the preserved trees hinting at the weather during the era of the Mongols.

Not to worry anyone, but as the New York Times recently reported, the Mongolians might be stocking up for the big push:

These days, the perks are far plusher. Mongolia, it turns out, sits atop a treasure trove of copper, coal and gold that is changing the fate — and the face — of this mostly empty country, thanks to China’s insatiable demand for natural resources. The surging mining trade has made Mongolia the world’s fastest-growing economy, transforming Ulan Bator into a city where Soviet bust meets Chinese boom.

And now the mercenaries in finance, attracted by a frenzy of deal-making, have joined in, too. “It’s a bit of a gold rush,” Mr. Hodgson said as he worked a booth at a coal industry conference packed with tailored suits and foreign accents.

For locals, their gentrifying capital, home to half of Mongolia’s 2.7 million people, has become a petri dish for their hopes and fears. Amid the crumbling Stalinist apartment blocks and rising skyscrapers, a debate is raging over mining’s impact, pitting those who praise the industry for sweeping away decades of decay against others who see materialism and corruption polluting Mongolia’s traditional way of life.

Sure, the Mongols might look cute and cuddly, but one minute they’re tending sheep, the next they’re chucking plague-infected carcasses into besieged cities.