Population dispersion was much different and you can't Judge ruthlessness by how many died. That's no measuring stick. Very few ever thought of crossing Ghengis kahn for a reason.
Dont forget though that the United states and the allies helped him by forcing people onto trains to be repatriated behind the iron curtain that they knew were going to be executed and enslaved. some of them were not released until the fall of the USSR.
The guy blew up a entire planet just to send a message...
The bottom guy had it so good that one out of every 4 of his countires citizens died during his revolution and rule!
Genghis Khan killed about two million and many at one time but sure doesn't hold the record.
Mao also had his share.
that's a good one