It's the same concept as a monopoly, if you're the sole supplier of a necessary substance or commodity, you can set whatever outlandish boundaries you want on it. Now, apply that if you can to government, begin to imagine the sort of power one authority would have when given the entire world to govern. The irony is that people hypothesized there would be peace and tranquility under the Absolative banner, but it only gave way to a new level of strife and atrocity.
The Absolatives found themselves in a position where they were making the decisions that governed the planet, but while the majority supported them there were still those who had difficulties or misgivings about everyone putting their chickens in one pen. It began like this, quiet discontentment giving way to protest, demonstrations, loud voices who claimed they would not be silenced. These claims were soon proven wrong.
In an effort to maintain order, the Absolative party called for mass incarcerations of the protesters. Most of those who were put into the prisons simply starved to death, swept under the metaphorical rug to be forgotten. These were the first martyrs in what was soon named the Partalitist movement. The Partalitists argued that multiple governments helped to maintain accountability and honesty, meaning that no matter how strong one power got, the rest could always band together and put a stop to them, if necessary. This new ideology was not received well by the Absolatives.
The leader of the Partalitist movement was assassinated not long after the announcement of their mission statement, her bullet ridden body discarded on the streets where she fell. The rationale was that order needed to be maintained at all costs, even if it meant freedom had to take a side seat.
This was nearly half a century ago and with all of these good intentions, the Absolative party have paved themselves a road straight to Hell, and much of the world have gone with them. As far as the general citizenry is concerned, the Partalitists have been exterminated along with any notion of separate governing powers. For some time, the Absolatives have believed the same, that they were unchallenged in their rule.
But the Partalitists had the sense to employ concealment, for themselves if not for everyone else. They went into hiding, anywhere they could, working, planning, hoping that there would come a time when the world could return to some semblance of sense again and they would be free. This was fifty years ago and the world has set in a tenuous calm, but change is an evolutionary imperative.
The costs of the new order were high: most major cities as the world had known them were destroyed, then literally covered over and built anew. The Absolative party and their followers pushed on in their lives in the new, improved cities, and the secretive Partalitists found life to be far easier in the forgotten corridors of the cities that once were. Becoming the underground in a quite literal sense, they began to ban together, and then fight amongst themselves.
Six major gangs sprang up in the ghost city that had once been New York, all of them fighting for limited supplies, territory, and members. Their numbers slowly increased, stressing the limits of the underground and finally forcing a conclusion they all knew were coming:strikes against the upper city.
Technology is limited: While weapons and survival equipment is being constantly researched and developed, the resources for actually -making- these items are spread thin, and hard to get hold of. Other apsects of comfort have deteriorated into nearly non existent. Problems that plagued settlers back in the horse and buggy era have returned-disease from contaminated food and drink, lack of basic or advanced health care, and a kill or be killed mentality make survival tough.
The gangs themselves have developed into tribe-like entities. While only the actual members go off to fight, their families group together under the gang's protection. These families-mostly children and the elderly, as women are expected to do their part in the gang- are moved frequently to keep their location secure from those above, and the other gangs as well.