The End is Now (The Apocalypse Triptych, #2)

by John Joseph Adams

revolutions are made by young people,

They fell back on animal instincts. Flight or, far more often, fight. Humans were predators by design, honed by two hundred thousand years of evolution into brutal hunters. Only the thinnest veneer of civilization lay on top of that. Strip it away, break down everything that made a person human, and what was left wanted very badly to punch you and scratch you and make you bleed.

Because the economic impact of the interstate system was huge. But they were secondary to military needs. Just like Rome.