Monsterland

Before Monsterland, most of the planet's monsters lived on a South Pacific island dubbed Monster Island. There, the beasts were detained for the sake of humanity, and also studied by the world's scientists. However, in 1973, underground nuclear testing destroyed Monster Island, and the small landform was rendered uninhabitable. Within a few years, however, the monsters were rounded up again and detained on a new island in the Ogasawara chain. This new island, dubbed Monsterland, contained a high-tech underground base from which the monsters could be monitored and studied.

Near the end of the 20th century, an alien race known as the Kilaaks seized control of Monsterland and unleashed the monsters across the globe under their mind control. The crew of the Moonlight SY-3 arrived on the island and encountered the Kilaaks, but were attacked by the Monsterland staff, who were also under the invaders' mind control. The SY-3 crew was able to escape, but Monsterland was left badly damaged and deserted.

After the monsters' mind control was later broken, and Godzilla and the Kilaaks defeated, the monsters were returned to Monsterland to live in peace.