History of Yama
The Enlightened Past (~30,00 years ago): This was a time of peace and harmony. Mankind was at his peak of achievement, and had even reached the stars. Technology would be considered “magic” today.
The Saurian Invasion (~20,000 years ago): The reptile-like Saurians invaded from Planet X. They enslaved the human race and built their great cities on top of the displaced humans.
The Kaiju Era (~12,000 years ago): The Saurians brought wild new (and dangerous) technology with them, this polluted the environment and caused the rise of the great monsters “Kaiju”. They were primarily responsible for the demise of the Saurian culture, and with their dwindling numbers from lack of food sources and a meteorite impact made it possible for humans once again to expand.
The Jomon Era (~5,000 years ago): The first city state to re-emerge was Jomon.
The Kofun Era (~2,000 years ago): The Kofun were invaders from distant Mu, they established the city of Kofu.
The Yamatai (Now): Yama is the current city-state and adventuring locale. The city is built over 30,000 years of history and the underworld is ready to be explored.