Bab 911: Chapter 911: Childish

The Emperor of Esteria allowed the Beastkins to come to his world. He not only allowed them to come, but he also gave them a faraway continent to populate. He didn't care about the citizens of that continent.

The Beastkins created their home in this new continent and started ruling that place. They used the humans of that continent as slaves, which they ruled over. The Esteria Emperor didn't care about this and let them do as they pleased.

Their rule lasted for a long time until the appearance of the Saint King, who not only defeated them but even Defeated the Emperor of Esteria.

They were once again forced to leave the world. That's when they found the world, which they started calling the Beast World. 

Thus, the Beast World had the original enmity with the Lightning World, which they had to live with since they couldn't openly wage war. There had been many short arguments and battles between the two after that but never a full-on war like the first time.