Another fine example were the Mongols. They achieved a lot with very few soldiers. They also left mountains of skulls (literally) and cities where they murdered

Another fine example were the Mongols. They achieved a lot with very few soldiers. They also left mountains of skulls (literally) and cities where they murdered everything (including animals) in their wake. Suffice to say, after a while nobody wanted to fight the Mongols. The subjugated did what they were told, because anything was better than the alternative: they might keep your prettiest daughters as sex slaves (if the daughters were lucky), kill you and all other members of your family, kill your dogs, kill your cows, kill the chickens, and then burn down the entire city for kicks. Maybe they even killed the rats. Then they'd send back a scouting party a couple days later to execute any survivors who someone escaped the first massacre.