Prior to the events of the anime, the
three factions - the
Garan Army, the
Kiba Army, and the
Hachiryokaku (
Aira Army), battle for total dominance of
Machine Island, which they occupy. The island is
basically a prison, isolated from the rest of
the world. To assure total
quarantine, a "Gravity Curtain was formed within the
island. Only machines created by the
worldwide government
WSO are capable of entry to the
island. The island also contains vast amount of
resources, allowing the
three factions to create a
near-limitless supply of
giant robots for their respective
armies.