Of all the remaining countries in this world the US has suffered the most. Decades of internal war have reduced the country to a rump state comprising most of the old Eastern Seaboard.
Following the Event the US collapsed into a period of anarchy made worse by the Living Death. Most of the bonds between states were broken and gradually about twenty small states were formed.
On the East Coast the anarchy that resulted allowed a far right group to seize power. Initially controlling little more than New York State the group declared that it was the legitimate regime for the whole country. Following this other extremist groups including the Ku Klux Klan seized power and created a state stretching from Boston to Florida.
The new states reprehensible racial policies led to war between it and the other states in the area which endured for more than thirty years.
Today the US is a single party dictatorship and is considered and international pariah.