To be fair, the Undergrounders couldn't remember why they fled to the buried silos in the first place. Something about a war, bombs that were dropped, pointless fighting that resulted in the decimation of millions of people. Whether the war had occurred world-wide or simply within their own borders was also unknown; with no major way to communicate outside of the immediate area, what was happening a world away was a mystery that too became plunged into darkness. Most of those who went to the surface in order to explore never came back, and survival required a certain type of elective ignorance. It made sense to not talk about what was going on above them: what did it have to do with feeding their children or building their battery stores?
What was obvious was the world directly around them: both above and below. Above, there lies a salted earth populated by savages who learned nothing from the warring of their ancestors. Plants will only grow with the greatest of concentrated effort (and even then, effort could only grant you so far with damaged soil and little water to speak of), and the hunger, heat, and poverty drive even the most patient savage insane. No wonder they've lost their minds! Children do not go to school (as there's not a school to be found), and only in the largest of cities can law enforcement be found. It's a land of lawlessness and mystery, something to be feared. Countless Undergrounders have found themselves enamored by the vastness of the Above - and have found themselves dead or enslaved as a result.
Below, the story is different. The people of the Below are the descendants of only the smartest, most resourceful people. Those who fled underground to find shelter from the bombs and the extreme heat that followed built a thriving society! The Undergrounders developed culture, created a safe environment to raise one's children, and allowed what was left of the pre-war technology to be adapted to the conditions. A price was paid for safety: cold, damp, and dark surroundings are of course a small price to pay in order to stay safe in a safeless world. The only options are the shelter of the Earth or the madness from above: it's your choice, and it's not a hard one to make.
Underground, the survivors of the war over 310 years ago have built a thriving society. Some of the original silos have been broken down, tunneled around, and grown into a bustling (and slightly overpopulated) metropolis. Batteries powered by waste and massive generators that threaten to shake one out of their skin power the cities with high dirt roofs; the brightest lights are located at the center of town, and the apartments in which one lives are the dimmest. Over time, the Undergrounder's eyes have adjusted to such a darkness. Scavving parties (groups of younger teens who go aboveground at night to scavenge for parts) boast that the moonlight of the Above is too bright for their sensitive eyes. Some silos have even tunneled so far in one direction that they've connected with other silos, marking the first time in hundreds of years that the Undergrounders have made contact with one another. They cling to the things that made pre-war times so great, the dances, styles, music, and culture: in a way, the people who live underground live in the past. They like it that way. And they like to keep it a secret. Only once has an Abovegrounder discovered a silo, a few generations ago...the entire silo was raided by bloodthirsty Abovegrounders, their resources stripped and their people killed. Most Undergrounders highly doubt the truth of this cautionary tale - but it COULD be true. And the fear of that is more than enough to keep most Undergrounders lip's sealed.
Now, Above ground, the people have survived by the strength of their backs alone. They were not protected by the cold silence of the dirt and earth: instead, the people who would later become the Abovegrounders were the survivors of the original bombs. They fought the invading troops who came to destroy the land and buildings after the dirt cooled from the initial blast. They stole the guns, fought back, and won what little shred of land might have been left. These are the battlemongers, the rough and dirty scars of what happens to a lost humanity. Some more well-off Abovegrounders founded what they liked to call the "Industries" - thick-walled societies built around a safepoint where one could bring their families for some semblance of order. Industries had it all (or as much as one could have Above) - sturdy shacks, police, even a small collection of businesses that sold luxuries such as food, clothing, and weapons. Resturants are popular here as some industrious businessmen and women have found creative ways to make Coyote palatable.
But for the majority of the Abovegrounders, living in the Industries (or the relatively safe surrounding areas called Sub-industries) is not a possibility. Most of them are simply too poor, not talented enough to make themselves useful, or too unlucky to be born there. So, where do they all live?
The Badlands. So what constitutes a Badland exactly? Cracked, sandy earth, very few buildings (after all, Badlanders tend to kick families out of their homes to create a hub for their crimes), and all-out lawlessness. Badlander children shadow their parents to learn the ropes, and after some time, pick up the family "business" (whatever that may be). Most Badlanders make a living by scrapping: going to old, destroyed cities and strapping materials to their backs (or to the backs of their families) and hauling it all back to the Industries for payment. Most of those elderly who "make it" to the Industries scraped by and saved their way in in exactly this fashion. But, for those who are Badlanders and like it that way, there's many other forms of employment: thievery, trickery, and rowdiness. A Badlander can find relative wealth via means of becoming a roadside bandit, and some even band together to become compounds.
So why on earth would the two societies whom are either unaware of despise each other come together? Sometimes, all it takes is a single forbidden romance to change the world. Whether it were for the better or for the worse however? That remains to be seen.