At the fall of Earth and the formation of the Republic, the USA, Asia, and parts of Europe dominated the future's culture. The people that left witnessed leaving people behind, friends, families, loved ones-- the government made a mistake in dropping experimental bombs. They could fix it. It was just a matter of moving elsewhere. No problems there.
Right?
The resulting citizens came from many backgrounds, ways of life, and beliefs. Some people were left behind, in the radioactive, bombed wasteland of Earth. The people that were born afterward, and didn't leave on the rockets and colony ships, were lead to believe that Earth is nothing but a black rock.
The year is 2380. Everyone, rich and poor, is effectively bi-lingual in Basic (required in Core Worlds, at the request of "common communication") and another language. Common languages include a Chinese/Japanese hybrid, as Asia united near the "end" of Earth, and Mageran. Mageran usually only peppers conversation; others speak it fluently.
Advertising and marketing are rampant, from the sides of space stations, to bars, sides of buildings, to the VRNet.
As Earth's authority and usefulness crumbled, corporations did well to take advantage and establish themselves in the early chaos. From this, they rose into authority alongside the Republic, and therefore allied with it. It's to be expected that if they are co-owned by the Republic, they are everywhere, and they are powerful.
The Republic's utopian ideal has terraformed and united the Core worlds under one government. The Mageran Empire, consisting of Xel Kyan, Var Saaj, and Geneva, among other planets, caused friction with this expansion. Peace talks have done little but alleviate a war from occurring...again.
Many were lead to believe that Earth no longer exists; terraformed planets are far enough away to believe that it isn't. There is not a soul that willingly enters Earth alone, if at all, and therefore if it is mentioned in conversation, the person is thought insane. Some that lived there, and continue to, know that its existence is very real. Sad, but real, and a never-ending conspiracy. The only signs of life left on Earth are Wraiths, rampant souls of the mutated and the dead, which wander over the scarred surface of the planet, picking off citizens, drifting continent to continent endlessly. Small towns stand defenseless, as the Republic fails to respond to distress calls that the Republic caused.
The further out from the Core one lives, the harder life is.
Core Worlds, Outer Worlds, Wild Space