History of the three earths
At the dawn of man was the age of myth, when magic first came upon the world. This became the first great tool for humanity as it began its first steps into civilization, as the first magi began to unravel its mysteries. However magic itself is a living thing and would choose avatars in its own fickle ways; these would be the first of the gods. Man and beast alike, who unlike the magi who wielded supernatural power through study and wrote, could wield magic and bend the world itself to their whim as easily as they breathed, and would terrorize the world with their terrible might. While not all were malicious they were enthralled with their power and limitless as it was, and as easily as they could raise a civilization into paradise on a mere whim they could just as carelessly dash it into oblivion. The Magi, Shamans, Wizards, Druids, Brujah, and many more stood as the only shield against the gods capricious moods and the damage in their wake, and in doing so many became close councilors of the gods, or even honorary gods. However despite their efforts the magicians of the world could not save humanity as they were; their knowledge and number were too scattered and the task before them too overwhelming; that is until a certain discovery was made, the leylines. it had been long understood that magic traveled in some fashion often being compared to wind or currents, but until -insert name here- no one had thought to map them, as even the concept of a map was relatively new. But when they did they found that when strong enough of these currents meet they form pools of great power, but more importantly that each of these pool had a unique resonance to them, and that when you used that resonance in a different pool on the same line it would replicate in the corresponding pool! This power of telecommunication would allow the magicians of the world to commune with each other irrespective of the vast distance between them, and would allow the knowledge of the world condense, and eventually they realized they could begin a ritual to free humanity from the tyranny of the Gods all together. Now how this ritual was actually able to be created is hotly debated. As in theory the magical understanding of the ancient magicians should have been too primitive to accomplish their ultimate goal, and yet they did. Many theories surround this event involving everything from lost precursor civilizations, alien influence, sheer luck, and even the insight of friendly gods (from which their is no shortage of claimants: Hermes, Diana, Odin, Thoth, many of the Buddhas or Vishnus, any combination of the previous and many more), but whatever the case for reasons soon to be discussed the truth is lost. However it was done aside when their work was done they had the ultimate sealing ritual: the seal of an empty earth. It bound the gods using their very own natures against them sealing them outside of reality in an inversion of earth where the ground and sky themselves switched their places leaving them entombed within a Hollow earth. And with magical wards and channels cleverly placed so that any attempt to escape their prison would see their power sapped and redistributed strengthening the wards against any other potential escapee. The cleverest trick trap though was in how hospitable the gods new home was, as any god who used their power to enhance the protections of the Hollow Earth would see their control over the domain within increased exponentially, which left many of the trapped gods content with their new existence, but not the majority.
While the seal of the Hollow Earth is formidable it was not unconquerable, and shortly the magicians found themselves against a horde of angry gods. This was the final battle of the age of Myth and little is known for sure about it as much of the world and its magicians were nihilated in its brutality. It very well might have been the end of the world if the gods were not weakened by the journey from their prison stripping of them the greater part of their omnipotence and the power of seal pulling them back within the Hollow Earth should their focus and power wane. But with the war over and the gods by and large sealed the age Myth would end and the age of legeneds and human civilization should truly begin. Humanity now able to truly able to begin civilization quickly flourished and none more so than the mage cities founded from the remnants of those who sealed the gods on and built on the leylines that granted them unity. Though this was not an era entirely without their influence, as seen with godswar that preceded this era a god could descend to earth and meddle as they willed if in a weakened state and unfortunately as the gods became more used to their new home their became fewer reasons for them to descend to earth but to wage wonton violence. And while the magicians of this era were up to the task of dispatching these rouge gods, they faced their own self inflicted problem the Hollow Earth capped their magical potential. The seal of an empty earth you see works by scanning the earth for those with a certain level of connection and intermingling with magic that would label them as a god, and a magician can in theory temporarily achieve those heights and as such be sent to the hollow earth; this is not usually desirable as the pantheons carry quite the grudge against magicians and often see them smited on sight. Additionally the qualification for a being to considered a "god" by the seal was much lower than the actual lower bound of what a god was actually capable. The mage cities consulted amongst themselves through leylines for many centuries as they studied seal to recover the lost knowledge of its construction and in doing so came to a solution to both their problems: the firmament. A variation of the SoaEE it created a flat barrier between the two earths formed from the land and leylines surrounding the magical cities of the world interposing themselves between the gods and earth while also freeing them from the gaze of the SoaEE allowing them to practice their sorceries freely with no limit on this new Flat Earth. And as such magical metropolis around the world that stood as the pinnacle of civilization one day such as Atlantis, El Dorado, -insert list of lost magical cities here- appeared to sink away from the world only tp reappear in the world between. However these two great seals had a side effect and saw much of the magic of the original earth siphoned away to the other worlds, and as such the interest of the gods and magicians alike of the mundane world. Magic and magicians did persist there sure but only in pale imitations of the other earths and the age of legend and even magic itself there faded until nearly forgotten as the years rolled on and mundane man looked to the inventions of science for its future. Then there were Nazis and everything would change again.
Both world wars saw significant occult influence, even if not publicly, both intentionally or unintentionally. As mans understanding of science and the rules of nature improved they also began to pull at things that had been sealed behind the protections of the other worlds, and this would begin to bend the magical worlds in ways unintended until something finally broke. Known just as the hole to the magically inclined a rip was pulled in the fabric of the magic worlds reality that let magic flood back into the mundane world which would be responsible both for the technological acceleration of the coming century and the introduction of the superhuman to the modern world. Magic would once again choose avatars amongst the human population creating a new form of god now just called superhumans due both to the areligious nature and due to being significantly weaker than their godly siblings. But its not magics chosen that would become superhuman in the modern era as the magic traditions that remained in the mundane world found themselves empored as they never had before, and with whole new understanding of science mixed with magic induvials find themselves blessed with flashes of insight into the nature of the world able to produce artifice and serums unreplaceable by anyone but them due to their specificity and esotery. The gods also found newfound access to the mundane world but as a whole find little interest in it as their ire mostly lies with the magicians of the Flat Earth for imprisoning them and the Flat Earth is much the same from the opposing direction. However the bored, ambitious, and occasionally the benevolent will involve themselves in mundane affairs if it suits them.