Paul Di Filippo has written a masterful, lively history of the many ways in which science fiction has explored the collapse of the American project, from JA Mitchell's 1889 The Last American to contemporary novels like Too Like the Lightning, Liberation, DMZ and Counting Heads.
The Last American by J. A. Mitchell from 1889 finds the country a barbaric wilderness shambles, subject to a condescending visit from representatives of the civilized Middle East. The protagonist of M. P. Shiel's The Purple Cloud (1901) emerges as, literally, the last man on the planet after a noxious celestial gas attack, and happily burns down the world's great cities for sociopathic fun, including San Francisco. Some of these narratives played up racist fears: Philip Francis Nowlan brought the country low with Asian "Han" invaders in 1928's Armageddon 2419 A.D., the basis for the Buck Rogers franchise, and Robert Heinlein followed suit with an Asiatic menace in 1949 with Sixth Column. A new plague does the trick of dismantling the country in George Stewart's pastoral Earth Abides (1949). Omnipotent alien Overlords upset all existing geopolitical realities in Arthur C. Clarke's Childhood's End (1953). In Leigh Brackett's The Long Tomorrow, from 1955, after a devastating war the USA's amended Constitution prohibits any large-scale settlements, leaving the country a rural backwater. Edgar Pangborn's Davy (1964) conjures up a scenario similar to aspects of both Stewart's and Brackett's. And of course, Philip K. Dick's The Man in the High Castle (1962) looked back to imagine a country divided between the Axis conquerors. Germany and Japan.
While there have been numerous stellar books after Davy that utilize these same bugbears to undo the USA, one particular kind of national collapse rose to prominence in speculative fiction in the mid-1960s: the internal fragmentation or disunion or balkanization of the country, due solely or mainly to systemic or regional or contentious cultural forces. No foreign soldiers, no microbes, no bombs, no bug-eyed-monsters need to be involved. The dissolution of the Union happens strictly due to internal contradictions, forces and factors that compel a splintering or segregation, whether mutually agreed upon by all parties, or unilaterally enforced by some. (And, surprisingly, sometimes the new situation is an improvement.)
This scenario, of course, bears increasing relevance in our culturally and politically divided moment and beyond, and one might predict a growing number of such tales.
Disunion: Visions of Our Fragmented Future [Paul Di Filippo/Barnes and Noble Review]