> Having invaded, destabilised, and collapsed most of South America and other parts of the world, all that is left is for America to destabilise itself

Looking back at history, it's not surprising. Every big empire goes down the same way, by destabilizing and tearing itself up.

The Roman Empire, the Mongol Empire, the Byzantines, the Ottamans, everyone went down the same route. Now of-course with the nukes in question the USA might not just break itself up into pieces, but it definitely might exist only as a shadow of itself.