Old World
From Little Tail Wiki
The Old World refers to Earth before the activation of the "Reset" command. Many of the humans portrayed throughout Little Tail Bronx come from the Old World, with some Hybrids also previously living within it before they reawaken in the new world.
History
The Old World's history always begins with the discovery of Juno in the early 1970's. When Juno was realized as an extremely powerful energy source, many countries had begun dividing Juno amongst each other in order to prevent a power struggle. A group of incredibly intelligent researchers named the XII Owls would also be formed during this time. All of these efforts would prove ineffective, however, as Juno would become the sole cause of World War III.
The war was the most catastrophic event on Earth, with many countries pitting their Titano-Machina against each other. The Vanargand would prove to be one of the deadliest weapons at this time. As the war went on, much of Earth had already been laid to waste. Currently, it can be assumed some European countries had caused most of the damage. Other notable Titano-Machina used during the war were Lares, Lemures and the Iron Giant.
During this, a presumably French-based group of researchers would begin inventing pseudo-Juno weaponry in order to combat those abusing real Juno. This lead to the creation of the Taranis, a tank capable of one-shotting even the largest Titano-Machina at the cost of one's life. After successfully taking down the Vanargand, the Taranis would be sealed within the Earth by the Juno. The tank's personality OS, Jeanne, would malfunction at this time.
The XII Owls, based at Australia's Futzu Tower, had a trump card up their sleeve for such a disaster, which was their "Reset" command. Once things had come to a head, the command was activated and wiped all living beings off of Earth. A byproduct of this was launching large chunks of the Earth into the sky and creating a highly deadly layer of electricity between the ground and the newly formed sky islands.
2000 years after the Reset, a surviving group of humans would begin building Belenos and creating artificial humans to power it, bringing life to Jiru in the process. How they survived or where they were based at is unknown.
In modern times the Earth, now known as the Old World, is nigh impossible to access. A sky whale named Nushi is the only known method of travel between the sky islands and the Old World, however its life span is currently stated to be waning.