Okay, if I remember
my secondary source correctly (scroll to page 105), the Soviet Union succeeds in developing a laser-based ABM system, and Arslan (the leader of "Turkestan") compels the Soviet leader at gunpoint to demand the surrender of the United States. As for his plan, he appears to want to return the United States to a sort-of 19th-century level as part of his general critique of the greed and shallowness of contemporary American society.
Sounds pretty stupid, I know. But from what I've heard, the novel actually does a decent job in exploring how a conquered people relate to (and, eventually, come to love) their occupier.