"Yes, he did attack other herds," Cleve said. It seemed to be an extreme understatement, but Cleve found no better words, "Humans, our species, is divided into races and nations. Races are made up of humans who share a similar characteristic, like blond hair and blue eyes, for example. Nations are made up of a single or multiple races living in a single place, kinda like the Great Valley. Hitler attacked other nations and races."
"Like the fast-biters from the Mysterious Beyond taking over the Great Valley and eating all the leafeaters?" Ruby asked.
"Precisely," Cleve replied, glad that he manged to explain the concepts clearly, "And that's way we need to stop him."