Now's the time for Atlas living at the "top of the world." - Atlas is the newest kingdom to be created, and considered one of the most successful - Atlas did not exist before the Great War. Back then, it was Mantle, on the continent of Solitas - Atlas is mostly frozen (as if you couldn't tell from the map), yet this actually worked to the people's advantage since the harsh weather conditions kept the Grimm away. - In order to survive, they dug underground (presumably to take advantage of geothermal heat) and discovered Dust, utilizing its power for their survival, and they were pioneers in this field (which we could guess considering SDC is in Atlas) - During the Great War, much of their attention towards energy research was switched over to weapons and military R&D, particularly by its combat school Austius. - After the Great War, Austius was converted into Atlas, and many amenities were added to the school's campus to provide for soldiers returning from battle, and build its own community, including residential areas. Over time, the military and its scientists moved in. - After a while of having the City of Mantle living under Atlas' shadow, the capital of the kingdom was moved to Atlas, and the transition from Mantle to Atlas was complete. Atlas continued on in prosperity, while it sounds like Mantle suffered and was left behind. Not exactly what I had in mind for the fall of Mantle, but I suppose it makes sense. I envisioned a military coup or Mantle being overrun by Grimm, forcing everyone to retreat to Atlas and build a new kingdom out of the ashes, one that was more of a police state than its predecessor in order to provide safety and security. Instead, it's a situation where Atlas was just more prosperous due to it being the center for military and technological advancement.