Welcome to Mega City 1!
The year is 2131.
There are 400 Million people living within the walls of the city, a city which stretches from Pre Atomic Washington to old Boston, from what was New York to somewhere called Philadelphia. One giant urban conurbation.
Outside the city… outside the city there is only death and the destruction. Following the Atomic wars of 2070 much of the world was laid waste, only a few cities survived. Thirty eight years later America has only four cities remaining, Texas City, Uranium City and Mega City two, on the west coast of America.
After that, take a look at your wiki. There is some more helpful info there.