The Fall of the Modern World
In the future depicted in planetarian, mankind depleted Earth's natural resources. Yet the human population continued to grow, reaching levels that an already-overtaxed agricultural system could not hope to keep up with. The United Nations at the time proposed a broad international initiative that was known as the Space Colonization Program. Looked upon as the only solution to all the problems that faced the world by many, it would have been an ambitious attempt to shuttle a majority of Earth's population into outer space, in search of suitable planets to exploit.
And for a short time, it indeed seemed that humanity would be spreading its wings toward the cosmos.
The Great War Begins
However, this was not to be. Due to a number of factors, the Space Colonization Program foundered. Riots broke out in all major urban centers of the world, as citizen battled citizen for resources that were becoming more and more scarce. At the same time, leaders of several nations -- world powers among them -- decided to initiate a bombardment of the major cities of their neighboring countries via satellite-deployed biochemical warhead-laden ICBMs. Those nations that possessed similar weaponry retaliated by launching similar bombardments on the offending countries, and those that did not retaliated by launching nuclear missiles.
Millions died in this opening fusillade of biochemical and nuclear arms, millions more died fleeing the stricken cities, and millions more died hastily erecting gigantic quarantine walls around the perimeters of those cities. Battles erupted at every location in the world, pitting man against man, man against machine, and machine against machine. Prior nuclear and biochemical disarmamentation treaties were thus proven to be not worth the paper they had been printed on as every nation participated in what amounted to nothing more than wholesale massacre. And this time around, unlike in previous wars, the privilege of neutrality was granted to no one.
A War Without People Left to Fight It
By the end of the first year of the War, the human population of the world had been halved. Every year for ten years, this number was halved again, and again, and again, and again. By the end of ten years, the nations that had initiated the orbital biochemical warfare bombardments that had touched off the War no longer existed. And yet the War, having taken on a life of its own, raged on.
The human armies of the world had rapidly become decimated in the conflict, so instead the surviving nations deployed autonomous battle mechs known as "Warmongers" onto the battlefields, along with autonomous hunter-killer tanks known as "Hedgehogs" and anti-personnel drones known as "Menschenjagers". Even when there were no human beings left to fight the War anymore, the fighting still continued ... for the point of the War had stopped being about the conquest of land a long, long time ago. Now humanity had nothing but the internecine creed of revenge and massacre to call its own.
The Final Massacre and the Aftermath
Little is known about this event, other than the fact that it was the thing that brought the War to a close. Of all the soldiers -- human and mechanized -- that dove into this fray, few indeed returned alive. Fewer still failed to succumb to the combination of their war injuries and the genetically-engineered bacteria that had grown rampant on the battlefields.
Many other things disappeared along with the death of most of the world's human population. The concept of a single standardized time was among the casualties, along with the concept of a census and the appreciation of fine art. The museums, centers of learning, and wonderous cities of the modern world were now but a passing memory as mankind strove to pull itself out of the grave that it had dug for itself.
The Rise of the Junkers and the Advent of the Rain
For a time, the few thousand human beings left on the Earth lived in relative peace, giving birth, for once, to children and not to weapons of enormous destructive potential. At the same time, adventurers began to delve into the ruins of the fallen cities, looking for still-functional remants of the old world -- things like MRE's, weapons, fuel cells, and especially cigarettes and liquor. They were labeled "Junkers" by the people around them, for they led their lives meandering from abandoned city to abandoned city, looking amidst the junk for things to sell.
And then, the Rain began to fall. Except it was like no rain that humanity had ever seen before. It fell continuously, blotting out the sun and obliterating the seasons. It killed the plants, poisoned the soil, dissolved concrete, caused steel to corrode and melt, and turned people into dead bodies.
The Plundering of the Sealed Cities / Planetarian Begins
One side effect that the Rain had, other than completely destroying the ecosystem on the Earth, was that it melted away in fairly short order the vast concrete sarcophagi that, like testaments to humanity's hubris, had enveloped most of what had been the major urban centers of the world before the War. These abandoned urban areas, known as sealed cities, quickly fell prey to the Junkers with the demolition of the quarantine walls. However, those Junkers who infiltrated their way into the cities found that they had made a dire mistake -- squads of still-functional Hedgehogs and roving packs of Menschenjagers still filled the streets of these dead cities.
... and in the very center of one of these sealed cities, there still stood a tall skyscraper, rising like a magical tower out of the darkness ...