There are many parallels between the USA and the USSR. The United States were forced to abandon the west coast as the Rocky Mountains turned into one of the world's largest red zones. The federal government will not give up on reunification, but their control is spotty west of the Mississippi, and nonexistent west of the Rockies, with California now all but independent.
Much of the Midwest is also approaching red zone status. A new dust bowl, firestorms, and a seven year cycle of locust swarms all compete to destroy vital farmland. Well-to-do settlements in these regions are built underground, protecting them from these many disasters. Most of these are typical bunker complexes, but the most distinctive are the silo towns, built in decommissioned nuclear silos.
Most major cities contain white zones in the form of domes or arcologies, the most well known of which are the Manhattan Enclosure, the National Mall, the Chicago Towers, and the Orland Stilts. Aside from the Rockies, the largest red zones are the Louisiana bayou, the Florida everglades, and many sections of the Appalachian mountains.
America refuses to be defensive. No established politician will publicly give up on reunification. The less able they are to guarantee internal security, the more aggressively they advocate it.