Ever since Humanity first crawled out of the mud, there were the Vermis. A humanoid, flesh-eating monster that mutated from the common earthworm. Since Humans learned to remember, they have feared the Vermis, kind of degrading, right? But there was a reason to fear them. The Vermis look exactly like humans, except that Vermis have white hair and have no gender. For humanity, the Vermis threat drastically slowed technological progress down for the past four thousand years, but then Humanity discovered Lifinium, a rare mineral that pushed against Earth’s gravity, therefore causing whatever was on top of it to float. With this knowledge, Humanity became able to escape the Vermis while having a permanent home. They built gigantic Cities surrounding Lifinium. By doing so, Humanity was able to control where they traveled while in the comfort of their homes.
As time progressed, Humanity was able to do other things besides just surviving the Vermis. They declared war on the other Cities, determined to steal resources. The Cities could only be so large, forcing them to manage their space effectively. So, if a city had too much firepower, they could attack more Cities, stealing their resources, but if they could not find another city they would starve. The Cities without much firepower quickly fell victim to the stronger Cities. Over the years the Cities were able to reach equilibrium, just enough firepower and just the right amount of agriculture.
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The wars between the Cities are continuous, leaving hundreds of thousands either wounded or dead. Many of the citizens despised the wars, but knew that they couldn’t do anything about it for fear of being banished and left for dead in the wilderness, with the Vermis and other horrific creatures. The Cities were very impressive, as the bottom and walls were made of steel, the Buildings were made of wood and stone. Because of all the dangerous creatures that roamed the land and sky, the Cities had a glass dome.
Mutations had spread through the land before Humanity even existed. Most Animals grew to gargantuan proportions, while the rest changed in many other ways. Bears continued to live unchanged, except their backbones stuck out of their hindquarters. Panthers grew exponentially, eventually becoming capable of carrying people. Humans, without knowing, had also mutated, but much slower, and much more diverse.