During the Second Nano War, nanotechnology ran rampant over continental Europe. Rival nanobots modified the bodies of the inhabitants (human and otherwise) into various configurations, most of which were originally designed for battle. As the resultant organisms tended to resemble monsters from human mythology, they are loosely referred to as demons.
The conversion of Europe into “Hell” took several years. Some of the wealthy population of Western Europe was able to flee, though the poor were left to face the demons and clouds of nanoconverters. Of particular note, a good deal of the upper class of Great Britain relocated to the east coast of America, contributing to the tenor of the Empire of America.