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.
Quite true. However, the armies that made it as far as Central Europe were much smaller in size, breaking up into groups as small as the 20,000 I mentioned, or even smaller, but recombining as needed to fight major battles.
There is a persistent myth that the Mongols had huge armies, which is why their name for their armies, horde, came to mean a huge number.
In actual fact the Mongols were almost always considerably outnumbered by their opponents, though it probably didn’t seem that way to the opponents! The Mongols won by speed and maneuver instead of brute force, concentrating their forces quickly to achieve superiority at a critical point rather than across the board. The Mongols practiced a horse-powered version of blitzkrieg many centuries before WWII.