Many millennia ago, long before the reign of the Six Ancient Warriors, the single terrestrial planet of Old Vestroia split into 12 separate worlds under mysterious circumstances, thus dividing its population into 12 parts. Over the course of a few thousand years the primal inhabitants of Old Vestroia's attributed worlds had evolved in order to ensure a better chance of survival.
The evolution process resulted in the creatures taking on the characteristics of their surroundings, thus creating Attributed Bakugan. The Twelve Primal Attributes were also known as Aquos (Water), Pyrus (Fire), Haos (Light), Darkus (Darkness), Ventus (Wind), Subterra (Earth), Glacies (Ice), Metallum (Metal), Virus (Poison), Natura (Nature), Fulgur (Lightning), and the Plasma Attribute.
Originally the twelve dimensions co-existed in a kind of symbiosis, maintaining the balance of positive and negative power with each other's Elemental/Attribute Energy, so the Perfect Core was not required.
However, one day Old Vestroia collided with a gigantic orb of pure negative energy from the depths of space, awakening bloodlust and desire for conquest deep inside the Bakugan's hearts, causing a global war to break out amongst them. The war lasted for centuries, and many were slaughtered. The Attribute Of Natura completely ceased to exist, while other Attributed Worlds suffered heavy losses.
However, the Bakugan continued to evolve even in those harsh conditions, and the strongest of the strong eventually gained the ability to neutralize the effect of the Negative Energy. One of the first ones to break free of the curse was Plasma Kirin, the most powerful warlord of Old Vestroia and the ruler of the Plasma Dimension. He realized that someone had to put a stop to that madness. Using his power, he syphoned off as much negative energy as he could and took the full brunt of it, resulting in the eventual destruction of his physical body. However, the complicated magical ritual that was required to syphon off the energy also caused an extremely powerful force field to appear right in the middle of Old Vestroia, separating the 12 worlds into two groups of 6 and sealing Plasma, Glacies, Metallum, Virus, Fulgur and the now barren Natura Realm away from Pyrus, Aquos, Subterra, Haos, Darkus and Ventus. It also created a pocket dimension, Caliban, between the two separate worlds. Following the separation procedure, Plasma Kirin disintegrated and died, taking the negative energy and the horrible curse to the grave with him. His bodiless spirit, along with the remnants of his Attribute Energy, transformed into the first Perfect Core that would maintain the balance of positive and negative energy in Vestroia, while the six Lost Attributes were forced to exist without a core. Nobody knows what hads happened to the Lost Attributes, but it is possible that the six sealed dimensions have been ravaged by countless wars due to the imbalance.
Centuries have passed since that time, and Kirin's heroic feat and it's devastating side effect were lost to legend, so modern-day Bakugan are convinced that Old Vestroia split into 6 attributed worlds instead of twelve. It is highly likely, though, that some of the oldest inhabitants of New Vestroia are in possession of some knowledge about Vestroia's true origins, only they prefer to keep it a secret for personal reasons.