40 millions casualties is an impossible number. There
aren't millions of Mogol warriors, just tens or hundreds of
thousands. The conquest campaigns took years to cover the
vast geographical expanse - three Khans.
And there were little resistance considering the invaders were
running over villages and nomadic camps! The Mongolians were
good horsemen and archers and that explained their military
might. Also, there were fearless and wild used to wrestling
one another and going to rival camps to raid and rape. The
Han Chinese were terrified by such barbaric behaviour and built the
Great Wall. If you look at the length of the Great Wall, that
gives you an idea where the Mongols used to roam!
40 millions would be the population of the countries
conquered.
The extent of Mongol Empire (minus China) would be about the
same size as Soviet Union (USSR). And history had a
twist - Mongolia was a vassal state of USSR until recent
time. And USSR no longer exists!
But I think it happened back then bro coz I stumbled
upon it in wiki this is how it goes :
Before Genghis Khan died, he assigned Ögedei
Khan as his successor and split his empire into
khanates among his sons and
grandsons.[7]
He died in 1227 after defeating the Western Xia. He was buried in
an unmarked grave somewhere in
Mongolia at an unknown location. His descendants went on to stretch
the Mongol Empire across most of Eurasia by conquering and/or
creating vassal states out of all of
modern-day China, Korea, the Caucasus, Central Asian
countries, and substantial portions of modern Eastern Europe,
Russia and the Middle East. Many of these invasions resulted in the
large-scale slaughter of local populations, which have given
Genghis Khan and his empire a fearsome reputation in local
histories.[8]
Mongol campaigns may have resulted in
the deaths of 40 million people."[9]
Beyond his military accomplishments, Genghis Khan also advanced
the Mongol Empire in other ways. He decreed the adoption of the
Uyghur script as the Mongol
Empire's writing system. He also promoted religious tolerance in
the Mongol Empire, and created a unified empire from the nomadic
tribes of northeast Asia. Present-day Mongolians regard him as the
founding father of Mongolia.[10]