Robie Macauley’s 1979 A Secret History of Time to Come is a stand-alone post-holocaust novel.
It took surprisingly little time for American to divide itself into white suburbs and black (and other non-white groups) cities and to embrace increasingly extremist politics. The situation is unstable. By the 1980s, a gleefully genocidal civil war distracts the US from global affairs. Whereas the Soviets and Chinese could sit back and enjoy their new global dominance, neither is inclined to share. Across the planet, nuclear explosions begin to bloom.
Centuries later, the former United States is a very empty land.