Based on the estimates here:
<a href="https://en.wikipedia.org/wiki/World_population_estimates" rel="nofollow">https://en.wikipedia.org/wiki/World_population_estimates</a><p>Conservative estimates put the world population circa 1200 CE at 360,000,000. Optimistic ones put it at 450 mil.<p>If the estimates on Khan's 40mil are accurate, he killed anywhere from 9-11% of the global population.<p>Quite a feat to be able to say "One in ten people circa 1200CE were killed by Genghis Khan."