It has been nearly fifty years since the borders between states had become fences. Political divides had become so great that there were three types of states in the Ununited States Of America. Red White and Blue. Red had become the religious/conservative states, Blue had become secular/technology states and White were the few states left that allowed moderates of both. The White states are few and far between. Between all of the states there is a ten mile wide path that is federal controlled FreeLand that allows travel without venturing into the wrong state. The Red states suffer from overpopulation and lack of infrastructure. The blue are doing fine. In fact they are doing too well and conficts between the Blue and the Red in the border areas is increasing. There have been attacks between the Red and White states, but those have been mostly looting attacks on food transports. The attacks between the Red and Blue state border areas have grown into more than theft, there is now attacks that do not involve theft, only damage and casualties. the Reds blame the Blues, but it is only the Blues that are loosing people and supplies. It's pretty obvious what is happening. Obvious enough that the isolated Blue states are building defenses or being abandoned. The Fedral government is useless to stop it. There will be war.
It will be a short fight. Red has the population but Blue has the technology. Technology has never lost the day.