The Mongols went all the way to Germany.
But there weren’t 200M of them. More like 20,000.
The Mongols did, however, manage to kill roughly 10% of the world’s population. No other group has ever come close to that feat.
They also were far more efficient killers than the Nazis. The maximum output for a 24-hour day at Auschwitz was 24,000. The Mongols routinely killed several times that many people in a hour or so. All done with edged weapons.
Which pretty much blows a hole in the idea that mass killing requires technology.
Genghis Khan had many than 20,000 in his armies. In one battle he had 200,000 men.
Still far short of 200 million but I guess the creator of the universe knows more than I do.