Long ago, the first one to call herself the Demon King created Xaos. She united the various races of Evila to make their homes. It seemed that the Demon King delighted in “associating” with strong individuals.
The Demon King traversed the Demon World, and invited all the strong individuals she could find. Some people rejected the offer, but most knew who they were dealing with. She possessed an enormous amount of power, and was quite a beauty. Her appearance was flowing with elegance and she was also strong, with an overwhelming amount of charisma. There were few, if any, men who could refuse a request from her.
Basically, the Demon Lord’s gathered all the powerful and famous men in the Demon world and gave them a Harem. And so the offspring born during this time prospered and continued to live in the Xaos.
When the Demon Lord position was filled by a woman, men, and children of various races across the Demon World became united. As their descendants gradually increased, they slowly began to form what is known as a country. This is why the Evila, who did not believe in coexistence with other races, formed a country.