Before the Demon Emperor, the Demon Island was a forested area where various tribes, such as animal tribes, lived in separate groups using the most inferior and rudimentary technologies.
They lived by hunting the animals and beasts of the island, as well as the sea creatures that occasionally appeared alive on their shores.
Eventually, humans exploring the seas would catch up with them. They would become food for the demons when they arrived on the island.
But most of the demons rarely left Demon Island, and they didn't understand much about where these humans, who were so good for them to devour, came from. Only a tiny fraction of those who left the island made it to the mainland alive to wreak havoc in those lands and become much stronger.
In short, the demons lived isolated in that place, in the dark about various possibilities.
