World War IV. A war by humans, with an ending that no humans had possibly hoped for. The humanoid weapon system "Gears", which formed the primary battle force of any war-front,
went berserk on a massacre against humanity.
In a blink of an eye, most of humanity's civilization has been annihilated,
forcing the remaining survivors to live in underground shelters.
The berserk Gears were then called "RAGE".
Over time, humanity slowly regained control over several Gears,
and has now risen up to battle over the reign for the surface, against the RAGE.