The “External City” is a place in the future where a lot of people live. In the center of the city there is a big sphere like building that powers the whole area. Inside the sphere lives a endless source of renewable energy but how it exactly it came together I don’t know, you have to ask the scientists running the city. All the smart people around the world came to this place and trying to make it the garden of eden, a paradise on earth. New scientific discoveries followed up rapidly and because of this people lived luxurious and prosperous. The sphere got more and more powerful so people didn’t have to fight over oil and other sources that fuel mankind. But like all empires that came before, they rise and they fall, how this happened is a story for another time.